MILLER(1)

NAME

Miller is like awk, sed, cut, join, and sort for name-indexed data such as CSV and tabular JSON.

SYNOPSIS

Usage: mlr [I/O options] {verb} [verb-dependent options ...] {zero or more file names}

DESCRIPTION

Miller operates on key-value-pair data while the familiar Unix tools operate on integer-indexed fields: if the natural data structure for the latter is the array, then Miller's natural data structure is the insertion-ordered hash map. This encompasses a variety of data formats, including but not limited to the familiar CSV, TSV, and JSON. (Miller can handle positionally-indexed data as a special case.) This manpage documents Miller v5.3.0.

EXAMPLES

  COMMAND-LINE SYNTAX
    mlr --csv cut -f hostname,uptime mydata.csv
    mlr --tsv --rs lf filter '$status != "down" && $upsec >= 10000' *.tsv
    mlr --nidx put '$sum = $7 < 0.0 ? 3.5 : $7 + 2.1*$8' *.dat
    grep -v '^#' /etc/group | mlr --ifs : --nidx --opprint label group,pass,gid,member then sort -f group
    mlr join -j account_id -f accounts.dat then group-by account_name balances.dat
    mlr --json put '$attr = sub($attr, "([0-9]+)_([0-9]+)_.*", "\1:\2")' data/*.json
    mlr stats1 -a min,mean,max,p10,p50,p90 -f flag,u,v data/*
    mlr stats2 -a linreg-pca -f u,v -g shape data/*
    mlr put -q '@sum[$a][$b] += $x; end {emit @sum, "a", "b"}' data/*
    mlr --from estimates.tbl put '
      for (k,v in $*) {
        if (is_numeric(v) && k =~ "^[t-z].*$") {
          $sum += v; $count += 1
        }
      }
      $mean = $sum / $count # no assignment if count unset'
    mlr --from infile.dat put -f analyze.mlr
    mlr --from infile.dat put 'tee > "./taps/data-".$a."-".$b, $*'
    mlr --from infile.dat put 'tee | "gzip > ./taps/data-".$a."-".$b.".gz", $*'
    mlr --from infile.dat put -q '@v=$*; dump | "jq .[]"'
    mlr --from infile.dat put  '(NR % 1000 == 0) { print > stderr, "Checkpoint ".NR}'

  DATA FORMATS
      DKVP: delimited key-value pairs (Miller default format)
      +---------------------+
      | apple=1,bat=2,cog=3 | Record 1: "apple" => "1", "bat" => "2", "cog" => "3"
      | dish=7,egg=8,flint  | Record 2: "dish" => "7", "egg" => "8", "3" => "flint"
      +---------------------+
      NIDX: implicitly numerically indexed (Unix-toolkit style)
      +---------------------+
      | the quick brown     | Record 1: "1" => "the", "2" => "quick", "3" => "brown"
      | fox jumped          | Record 2: "1" => "fox", "2" => "jumped"
      +---------------------+
      CSV/CSV-lite: comma-separated values with separate header line
      +---------------------+
      | apple,bat,cog       |
      | 1,2,3               | Record 1: "apple => "1", "bat" => "2", "cog" => "3"
      | 4,5,6               | Record 2: "apple" => "4", "bat" => "5", "cog" => "6"
      +---------------------+
      Tabular JSON: nested objects are supported, although arrays within them are not:
      +---------------------+
      | {                   |
      |  "apple": 1,        | Record 1: "apple" => "1", "bat" => "2", "cog" => "3"
      |  "bat": 2,          |
      |  "cog": 3           |
      | }                   |
      | {                   |
      |   "dish": {         | Record 2: "dish:egg" => "7", "dish:flint" => "8", "garlic" => ""
      |     "egg": 7,       |
      |     "flint": 8      |
      |   },                |
      |   "garlic": ""      |
      | }                   |
      +---------------------+
      PPRINT: pretty-printed tabular
      +---------------------+
      | apple bat cog       |
      | 1     2   3         | Record 1: "apple => "1", "bat" => "2", "cog" => "3"
      | 4     5   6         | Record 2: "apple" => "4", "bat" => "5", "cog" => "6"
      +---------------------+
      XTAB: pretty-printed transposed tabular
      +---------------------+
      | apple 1             | Record 1: "apple" => "1", "bat" => "2", "cog" => "3"
      | bat   2             |
      | cog   3             |
      |                     |
      | dish 7              | Record 2: "dish" => "7", "egg" => "8"
      | egg  8              |
      +---------------------+
      Markdown tabular (supported for output only):
      +-----------------------+
      | | apple | bat | cog | |
      | | ---   | --- | --- | |
      | | 1     | 2   | 3   | | Record 1: "apple => "1", "bat" => "2", "cog" => "3"
      | | 4     | 5   | 6   | | Record 2: "apple" => "4", "bat" => "5", "cog" => "6"
      +-----------------------+

OPTIONS

In the following option flags, the version with "i" designates the input stream, "o" the output stream, and the version without prefix sets the option for both input and output stream. For example: --irs sets the input record separator, --ors the output record separator, and --rs sets both the input and output separator to the given value.

  HELP OPTIONS
      -h or --help                 Show this message.
      --version                    Show the software version.
      {verb name} --help           Show verb-specific help.
      --help-all-verbs             Show help on all verbs.
      -l or --list-all-verbs       List only verb names.
      -L                           List only verb names, one per line.
      -f or --help-all-functions   Show help on all built-in functions.
      -F                           Show a bare listing of built-in functions by name.
      -k or --help-all-keywords    Show help on all keywords.
      -K                           Show a bare listing of keywords by name.

  VERB LIST
     bar bootstrap cat check count-distinct count-similar cut decimate filter
     fraction grep group-by group-like having-fields head histogram join label
     least-frequent merge-fields most-frequent nest nothing put regularize rename
     reorder repeat reshape sample sec2gmt sec2gmtdate seqgen shuffle sort stats1
     stats2 step tac tail tee top uniq unsparsify

  FUNCTION LIST
     + + - - * / // .+ .+ .- .- .* ./ .// % ** | ^ & ~ << >> bitcount == != =~ !=~
     > >= < <= && || ^^ ! ? : . gsub strlen sub substr tolower toupper abs acos
     acosh asin asinh atan atan2 atanh cbrt ceil cos cosh erf erfc exp expm1 floor
     invqnorm log log10 log1p logifit madd max mexp min mmul msub pow qnorm round
     roundm sgn sin sinh sqrt tan tanh urand urand32 urandint dhms2fsec dhms2sec
     fsec2dhms fsec2hms gmt2sec hms2fsec hms2sec sec2dhms sec2gmt sec2gmt
     sec2gmtdate sec2hms strftime strptime systime is_absent is_bool is_boolean
     is_empty is_empty_map is_float is_int is_map is_nonempty_map is_not_empty
     is_not_map is_not_null is_null is_numeric is_present is_string
     asserting_absent asserting_bool asserting_boolean asserting_empty
     asserting_empty_map asserting_float asserting_int asserting_map
     asserting_nonempty_map asserting_not_empty asserting_not_map
     asserting_not_null asserting_null asserting_numeric asserting_present
     asserting_string boolean float fmtnum hexfmt int string typeof depth haskey
     joink joinkv joinv leafcount length mapdiff mapexcept mapselect mapsum splitkv
     splitkvx splitnv splitnvx
    Please use "mlr --help-function {function name}" for function-specific help.

  I/O FORMATTING
      --idkvp   --odkvp   --dkvp      Delimited key-value pairs, e.g "a=1,b=2"
                                      (this is Miller's default format).
      --inidx   --onidx   --nidx      Implicitly-integer-indexed fields
                                      (Unix-toolkit style).
      -T                              Synonymous with "--nidx --fs tab".
      --icsv    --ocsv    --csv       Comma-separated value (or tab-separated
                                      with --fs tab, etc.)
      --itsv    --otsv    --tsv       Keystroke-savers for "--icsv --ifs tab",
                                      "--ocsv --ofs tab", "--csv --fs tab".
      --icsvlite --ocsvlite --csvlite Comma-separated value (or tab-separated
                                      with --fs tab, etc.). The 'lite' CSV does not handle
                                      RFC-CSV double-quoting rules; is slightly faster;
                                      and handles heterogeneity in the input stream via
                                      empty newline followed by new header line. See also
                                      http://johnkerl.org/miller/doc/file-formats.html#CSV/TSV/etc.
      --itsvlite --otsvlite --tsvlite Keystroke-savers for "--icsvlite --ifs tab",
                                      "--ocsvlite --ofs tab", "--csvlite --fs tab".
      -t                              Synonymous with --tsvlite.
      --ipprint --opprint --pprint    Pretty-printed tabular (produces no
                                      output until all input is in).
                          --right     Right-justifies all fields for PPRINT output.
                          --barred    Prints a border around PPRINT output
                                      (only available for output).
                --omd                 Markdown-tabular (only available for output).
      --ixtab   --oxtab   --xtab      Pretty-printed vertical-tabular.
                          --xvright   Right-justifies values for XTAB format.
      --ijson   --ojson   --json      JSON tabular: sequence or list of one-level
                                      maps: {...}{...} or [{...},{...}].
        --json-map-arrays-on-input    JSON arrays are unmillerable. --json-map-arrays-on-input
        --json-skip-arrays-on-input   is the default: arrays are converted to integer-indexed
        --json-fatal-arrays-on-input  maps. The other two options cause them to be skipped, or
                                      to be treated as errors.  Please use the jq tool for full
                                      JSON (pre)processing.
                          --jvstack   Put one key-value pair per line for JSON
                                      output.
                          --jlistwrap Wrap JSON output in outermost [ ].
                        --jknquoteint Do not quote non-string map keys in JSON output.
                         --jvquoteall Quote map values in JSON output, even if they're
                                      numeric.
                  --jflatsep {string} Separator for flattening multi-level JSON keys,
                                      e.g. '{"a":{"b":3}}' becomes a:b => 3 for
                                      non-JSON formats. Defaults to :.
      -p is a keystroke-saver for --nidx --fs space --repifs
      --mmap --no-mmap --mmap-below {n} Use mmap for files whenever possible, never, or
                                      for files less than n bytes in size. Default is for
                                      files less than 4294967296 bytes in size.
                                      'Whenever possible' means always except for when reading
                                      standard input which is not mmappable. If you don't know
                                      what this means, don't worry about it -- it's a minor
                                      performance optimization.
      Examples: --csv for CSV-formatted input and output; --idkvp --opprint for
      DKVP-formatted input and pretty-printed output.

  COMMENTS IN DATA
      --skip-comments                 Ignore commented lines (prefixed by "#")
                                      within the input.
      --skip-comments-with {string}   Ignore commented lines within input, with
                                      specified prefix.
      --pass-comments                 Immediately print commented lines (prefixed by "#")
                                      within the input.
      --pass-comments-with {string}   Immediately print commented lines within input, with
                                      specified prefix.
    Notes:
    * Comments are only honored at the start of a line.
    * In the absence of any of the above four options, comments are data like
      any other text.
    * When pass-comments is used, comment lines are written to standard output
      immediately upon being read; they are not part of the record stream.
      Results may be counterintuitive. A suggestion is to place comments at the
      start of data files.

  FORMAT-CONVERSION KEYSTROKE-SAVERS
    As keystroke-savers for format-conversion you may use the following:
      --c2t --c2d --c2n --c2j --c2x --c2p --c2m
      --t2c       --t2d --t2n --t2j --t2x --t2p --t2m
      --d2c --d2t       --d2n --d2j --d2x --d2p --d2m
      --n2c --n2t --n2d       --n2j --n2x --n2p --n2m
      --j2c --j2t --j2d --j2n       --j2x --j2p --j2m
      --x2c --x2t --x2d --x2n --x2j       --x2p --x2m
      --p2c --p2t --p2d --p2n --p2j --p2x       --p2m
    The letters c t d n j x p m refer to formats CSV, TSV, DKVP, NIDX, JSON, XTAB,
    PPRINT, and markdown, respectively. Note that markdown format is available for
    output only.

  COMPRESSED I/O
      --prepipe {command} This allows Miller to handle compressed inputs. You can do
      without this for single input files, e.g. "gunzip < myfile.csv.gz | mlr ...".
      However, when multiple input files are present, between-file separations are
      lost; also, the FILENAME variable doesn't iterate. Using --prepipe you can
      specify an action to be taken on each input file. This pre-pipe command must
      be able to read from standard input; it will be invoked with
        {command} < {filename}.
      Examples:
        mlr --prepipe 'gunzip'
        mlr --prepipe 'zcat -cf'
        mlr --prepipe 'xz -cd'
        mlr --prepipe cat
      Note that this feature is quite general and is not limited to decompression
      utilities. You can use it to apply per-file filters of your choice.
      For output compression (or other) utilities, simply pipe the output:
        mlr ... | {your compression command}

  SEPARATORS
      --rs     --irs     --ors              Record separators, e.g. 'lf' or '\r\n'
      --fs     --ifs     --ofs  --repifs    Field separators, e.g. comma
      --ps     --ips     --ops              Pair separators, e.g. equals sign
      Notes about line endings:
      * Default line endings (--irs and --ors) are "auto" which means autodetect from
        the input file format, as long as the input file(s) have lines ending in either
        LF (also known as linefeed, '\n', 0x0a, Unix-style) or CRLF (also known as
        carriage-return/linefeed pairs, '\r\n', 0x0d 0x0a, Windows style).
      * If both irs and ors are auto (which is the default) then LF input will lead to LF
        output and CRLF input will lead to CRLF output, regardless of the platform you're
        running on.
      * The line-ending autodetector triggers on the first line ending detected in the input
        stream. E.g. if you specify a CRLF-terminated file on the command line followed by an
        LF-terminated file then autodetected line endings will be CRLF.
      * If you use --ors {something else} with (default or explicitly specified) --irs auto
        then line endings are autodetected on input and set to what you specify on output.
      * If you use --irs {something else} with (default or explicitly specified) --ors auto
        then the output line endings used are LF on Unix/Linux/BSD/MacOSX, and CRLF on Windows.
      Notes about all other separators:
      * IPS/OPS are only used for DKVP and XTAB formats, since only in these formats
        do key-value pairs appear juxtaposed.
      * IRS/ORS are ignored for XTAB format. Nominally IFS and OFS are newlines;
        XTAB records are separated by two or more consecutive IFS/OFS -- i.e.
        a blank line. Everything above about --irs/--ors/--rs auto becomes --ifs/--ofs/--fs
        auto for XTAB format. (XTAB's default IFS/OFS are "auto".)
      * OFS must be single-character for PPRINT format. This is because it is used
        with repetition for alignment; multi-character separators would make
        alignment impossible.
      * OPS may be multi-character for XTAB format, in which case alignment is
        disabled.
      * TSV is simply CSV using tab as field separator ("--fs tab").
      * FS/PS are ignored for markdown format; RS is used.
      * All FS and PS options are ignored for JSON format, since they are not relevant
        to the JSON format.
      * You can specify separators in any of the following ways, shown by example:
        - Type them out, quoting as necessary for shell escapes, e.g.
          "--fs '|' --ips :"
        - C-style escape sequences, e.g. "--rs '\r\n' --fs '\t'".
        - To avoid backslashing, you can use any of the following names:
          cr crcr newline lf lflf crlf crlfcrlf tab space comma pipe slash colon semicolon equals
      * Default separators by format:
          File format  RS       FS       PS
          gen          N/A      (N/A)    (N/A)
          dkvp         auto     ,        =
          json         auto     (N/A)    (N/A)
          nidx         auto     space    (N/A)
          csv          auto     ,        (N/A)
          csvlite      auto     ,        (N/A)
          markdown     auto     (N/A)    (N/A)
          pprint       auto     space    (N/A)
          xtab         (N/A)    auto     space

  CSV-SPECIFIC OPTIONS
      --implicit-csv-header Use 1,2,3,... as field labels, rather than from line 1
                         of input files. Tip: combine with "label" to recreate
                         missing headers.
      --headerless-csv-output   Print only CSV data lines.

  DOUBLE-QUOTING FOR CSV/CSVLITE OUTPUT
      --quote-all        Wrap all fields in double quotes
      --quote-none       Do not wrap any fields in double quotes, even if they have
                         OFS or ORS in them
      --quote-minimal    Wrap fields in double quotes only if they have OFS or ORS
                         in them (default)
      --quote-numeric    Wrap fields in double quotes only if they have numbers
                         in them
      --quote-original   Wrap fields in double quotes if and only if they were
                         quoted on input. This isn't sticky for computed fields:
                         e.g. if fields a and b were quoted on input and you do
                         "put '$c = $a . $b'" then field c won't inherit a or b's
                         was-quoted-on-input flag.

  NUMERICAL FORMATTING
      --ofmt {format}    E.g. %.18lf, %.0lf. Please use sprintf-style codes for
                         double-precision. Applies to verbs which compute new
                         values, e.g. put, stats1, stats2. See also the fmtnum
                         function within mlr put (mlr --help-all-functions).
                         Defaults to %lf.

  OTHER OPTIONS
      --seed {n} with n of the form 12345678 or 0xcafefeed. For put/filter
                         urand()/urandint()/urand32().
      --nr-progress-mod {m}, with m a positive integer: print filename and record
                         count to stderr every m input records.
      --from {filename}  Use this to specify an input file before the verb(s),
                         rather than after. May be used more than once. Example:
                         "mlr --from a.dat --from b.dat cat" is the same as
                         "mlr cat a.dat b.dat".
      -n                 Process no input files, nor standard input either. Useful
                         for mlr put with begin/end statements only. (Same as --from
                         /dev/null.) Also useful in "mlr -n put -v '...'" for
                         analyzing abstract syntax trees (if that's your thing).
      -I                 Process files in-place. For each file name on the command
                         line, output is written to a temp file in the same
                         directory, which is then renamed over the original. Each
                         file is processed in isolation: if the output format is
                         CSV, CSV headers will be present in each output file;
                         statistics are only over each file's own records; and so on.

  THEN-CHAINING
    Output of one verb may be chained as input to another using "then", e.g.
      mlr stats1 -a min,mean,max -f flag,u,v -g color then sort -f color

  AUXILIARY COMMANDS
    Miller has a few otherwise-standalone executables packaged within it.
    They do not participate in any other parts of Miller.
    Available subcommands:
      aux-list
      lecat
      termcvt
      hex
      unhex
      netbsd-strptime
    For more information, please invoke mlr {subcommand} --help

VERBS

  bar
    Usage: mlr bar [options]
    Replaces a numeric field with a number of asterisks, allowing for cheesy
    bar plots. These align best with --opprint or --oxtab output format.
    Options:
    -f   {a,b,c}      Field names to convert to bars.
    -c   {character}  Fill character: default '*'.
    -x   {character}  Out-of-bounds character: default '#'.
    -b   {character}  Blank character: default '.'.
    --lo {lo}         Lower-limit value for min-width bar: default '0.000000'.
    --hi {hi}         Upper-limit value for max-width bar: default '100.000000'.
    -w   {n}          Bar-field width: default '40'.
    --auto            Automatically computes limits, ignoring --lo and --hi.
                      Holds all records in memory before producing any output.

  bootstrap
    Usage: mlr bootstrap [options]
    Emits an n-sample, with replacement, of the input records.
    Options:
    -n {number} Number of samples to output. Defaults to number of input records.
                Must be non-negative.
    See also mlr sample and mlr shuffle.

  cat
    Usage: mlr cat [options]
    Passes input records directly to output. Most useful for format conversion.
    Options:
    -n        Prepend field "n" to each record with record-counter starting at 1
    -g {comma-separated field name(s)} When used with -n/-N, writes record-counters
              keyed by specified field name(s).
    -N {name} Prepend field {name} to each record with record-counter starting at 1

  check
    Usage: mlr check
    Consumes records without printing any output.
    Useful for doing a well-formatted check on input data.

  count-distinct
    Usage: mlr count-distinct [options]
    -f {a,b,c}    Field names for distinct count.
    -n            Show only the number of distinct values. Not compatible with -u.
    -o {name}     Field name for output count. Default "count".
                  Ignored with -u.
    -u            Do unlashed counts for multiple field names. With -f a,b and
                  without -u, computes counts for distinct combinations of a
                  and b field values. With -f a,b and with -u, computes counts
                  for distinct a field values and counts for distinct b field
                  values separately.
    Prints number of records having distinct values for specified field names.
    Same as uniq -c.

  count-similar
    Usage: mlr count-similar [options]
    Ingests all records, then emits each record augmented by a count of
    the number of other records having the same group-by field values.
    Options:
    -g {d,e,f} Group-by-field names for counts.
    -o {name}  Field name for output count. Default "count".

  cut
    Usage: mlr cut [options]
    Passes through input records with specified fields included/excluded.
    -f {a,b,c}       Field names to include for cut.
    -o               Retain fields in the order specified here in the argument list.
                     Default is to retain them in the order found in the input data.
    -x|--complement  Exclude, rather than include, field names specified by -f.
    -r               Treat field names as regular expressions. "ab", "a.*b" will
                     match any field name containing the substring "ab" or matching
                     "a.*b", respectively; anchors of the form "^ab$", "^a.*b$" may
                     be used. The -o flag is ignored when -r is present.
    Examples:
      mlr cut -f hostname,status
      mlr cut -x -f hostname,status
      mlr cut -r -f '^status$,sda[0-9]'
      mlr cut -r -f '^status$,"sda[0-9]"'
      mlr cut -r -f '^status$,"sda[0-9]"i' (this is case-insensitive)

  decimate
    Usage: mlr decimate [options]
    -n {count}    Decimation factor; default 10
    -b            Decimate by printing first of every n.
    -e            Decimate by printing last of every n (default).
    -g {a,b,c}    Optional group-by-field names for decimate counts
    Passes through one of every n records, optionally by category.

  filter
    Usage: mlr filter [options] {expression}
    Prints records for which {expression} evaluates to true.
    If there are multiple semicolon-delimited expressions, all of them are
    evaluated and the last one is used as the filter criterion.
    Conversion options:
    -S: Keeps field values as strings with no type inference to int or float.
    -F: Keeps field values as strings or floats with no inference to int.
    All field values are type-inferred to int/float/string unless this behavior is
    suppressed with -S or -F.
    Output/formatting options:
    --oflatsep {string}: Separator to use when flattening multi-level @-variables
        to output records for emit. Default ":".
    --jknquoteint: For dump output (JSON-formatted), do not quote map keys if non-string.
    --jvquoteall: For dump output (JSON-formatted), quote map values even if non-string.
    Any of the output-format command-line flags (see mlr -h). Example: using
      mlr --icsv --opprint ... then put --ojson 'tee > "mytap-".$a.".dat", $*' then ...
    the input is CSV, the output is pretty-print tabular, but the tee-file output
    is written in JSON format.
    --no-fflush: for emit, tee, print, and dump, don't call fflush() after every
        record.
    Expression-specification options:
    -f {filename}: the DSL expression is taken from the specified file rather
        than from the command line. Outer single quotes wrapping the expression
        should not be placed in the file. If -f is specified more than once,
        all input files specified using -f are concatenated to produce the expression.
        (For example, you can define functions in one file and call them from another.)
    -e {expression}: You can use this after -f to add an expression. Example use
        case: define functions/subroutines in a file you specify with -f, then call
        them with an expression you specify with -e.
    (If you mix -e and -f then the expressions are evaluated in the order encountered.
    Since the expression pieces are simply concatenated, please be sure to use intervening
    semicolons to separate expressions.)
    Tracing options:
    -v: Prints the expressions's AST (abstract syntax tree), which gives
        full transparency on the precedence and associativity rules of
        Miller's grammar, to stdout.
    -a: Prints a low-level stack-allocation trace to stdout.
    -t: Prints a low-level parser trace to stderr.
    -T: Prints a every statement to stderr as it is executed.
    Other options:
    -x: Prints records for which {expression} evaluates to false.
    Please use a dollar sign for field names and double-quotes for string
    literals. If field names have special characters such as "." then you might
    use braces, e.g. '${field.name}'. Miller built-in variables are
    NF NR FNR FILENUM FILENAME M_PI M_E, and ENV["namegoeshere"] to access environment
    variables. The environment-variable name may be an expression, e.g. a field
    value.
    Use # to comment to end of line.
    Examples:
      mlr filter 'log10($count) > 4.0'
      mlr filter 'FNR == 2          (second record in each file)'
      mlr filter 'urand() < 0.001'  (subsampling)
      mlr filter '$color != "blue" && $value > 4.2'
      mlr filter '($x<.5 && $y<.5) || ($x>.5 && $y>.5)'
      mlr filter '($name =~ "^sys.*east$") || ($name =~ "^dev.[0-9]+"i)'
      mlr filter '$ab = $a+$b; $cd = $c+$d; $ab != $cd'
      mlr filter '
        NR == 1 ||
       #NR == 2 ||
        NR == 3
      '
    Please see http://johnkerl.org/miller/doc/reference.html for more information
    including function list. Or "mlr -f". Please also also "mlr grep" which is
    useful when you don't yet know which field name(s) you're looking for.

  fraction
    Usage: mlr fraction [options]
    For each record's value in specified fields, computes the ratio of that
    value to the sum of values in that field over all input records.
    E.g. with input records  x=1  x=2  x=3  and  x=4, emits output records
    x=1,x_fraction=0.1  x=2,x_fraction=0.2  x=3,x_fraction=0.3  and  x=4,x_fraction=0.4
    Note: this is internally a two-pass algorithm: on the first pass it retains
    input records and accumulates sums; on the second pass it computes quotients
    and emits output records. This means it produces no output until all input is read.
    Options:
    -f {a,b,c}    Field name(s) for fraction calculation
    -g {d,e,f}    Optional group-by-field name(s) for fraction counts
    -p            Produce percents [0..100], not fractions [0..1]. Output field names
                  end with "_percent" rather than "_fraction"
    -c            Produce cumulative distributions, i.e. running sums: each output
                  value folds in the sum of the previous for the specified group
                  E.g. with input records  x=1  x=2  x=3  and  x=4, emits output records
                  x=1,x_cumulative_fraction=0.1  x=2,x_cumulative_fraction=0.3
                  x=3,x_cumulative_fraction=0.6  and  x=4,x_cumulative_fraction=1.0

  grep
    Usage: mlr grep [options] {regular expression}
    Passes through records which match {regex}.
    Options:
    -i    Use case-insensitive search.
    -v    Invert: pass through records which do not match the regex.
    Note that "mlr filter" is more powerful, but requires you to know field names.
    By contrast, "mlr grep" allows you to regex-match the entire record. It does
    this by formatting each record in memory as DKVP, using command-line-specified
    ORS/OFS/OPS, and matching the resulting line against the regex specified
    here. In particular, the regex is not applied to the input stream: if you
    have CSV with header line "x,y,z" and data line "1,2,3" then the regex will
    be matched, not against either of these lines, but against the DKVP line
    "x=1,y=2,z=3".  Furthermore, not all the options to system grep are supported,
    and this command is intended to be merely a keystroke-saver. To get all the
    features of system grep, you can do
      "mlr --odkvp ... | grep ... | mlr --idkvp ..."

  group-by
    Usage: mlr group-by {comma-separated field names}
    Outputs records in batches having identical values at specified field names.

  group-like
    Usage: mlr group-like
    Outputs records in batches having identical field names.

  having-fields
    Usage: mlr having-fields [options]
    Conditionally passes through records depending on each record's field names.
    Options:
      --at-least      {comma-separated names}
      --which-are     {comma-separated names}
      --at-most       {comma-separated names}
      --all-matching  {regular expression}
      --any-matching  {regular expression}
      --none-matching {regular expression}
    Examples:
      mlr having-fields --which-are amount,status,owner
      mlr having-fields --any-matching 'sda[0-9]'
      mlr having-fields --any-matching '"sda[0-9]"'
      mlr having-fields --any-matching '"sda[0-9]"i' (this is case-insensitive)

  head
    Usage: mlr head [options]
    -n {count}    Head count to print; default 10
    -g {a,b,c}    Optional group-by-field names for head counts
    Passes through the first n records, optionally by category.
    Without -g, ceases consuming more input (i.e. is fast) when n
    records have been read.

  histogram
    Usage: mlr histogram [options]
    -f {a,b,c}    Value-field names for histogram counts
    --lo {lo}     Histogram low value
    --hi {hi}     Histogram high value
    --nbins {n}   Number of histogram bins
    --auto        Automatically computes limits, ignoring --lo and --hi.
                  Holds all values in memory before producing any output.
    -o {prefix}   Prefix for output field name. Default: no prefix.
    Just a histogram. Input values < lo or > hi are not counted.

  join
    Usage: mlr join [options]
    Joins records from specified left file name with records from all file names
    at the end of the Miller argument list.
    Functionality is essentially the same as the system "join" command, but for
    record streams.
    Options:
      -f {left file name}
      -j {a,b,c}   Comma-separated join-field names for output
      -l {a,b,c}   Comma-separated join-field names for left input file;
                   defaults to -j values if omitted.
      -r {a,b,c}   Comma-separated join-field names for right input file(s);
                   defaults to -j values if omitted.
      --lp {text}  Additional prefix for non-join output field names from
                   the left file
      --rp {text}  Additional prefix for non-join output field names from
                   the right file(s)
      --np         Do not emit paired records
      --ul         Emit unpaired records from the left file
      --ur         Emit unpaired records from the right file(s)
      -s|--sorted-input  Require sorted input: records must be sorted
                   lexically by their join-field names, else not all records will
                   be paired. The only likely use case for this is with a left
                   file which is too big to fit into system memory otherwise.
      -u           Enable unsorted input. (This is the default even without -u.)
                   In this case, the entire left file will be loaded into memory.
      --prepipe {command} As in main input options; see mlr --help for details.
                   If you wish to use a prepipe command for the main input as well
                   as here, it must be specified there as well as here.
    File-format options default to those for the right file names on the Miller
    argument list, but may be overridden for the left file as follows. Please see
    the main "mlr --help" for more information on syntax for these arguments.
      -i {one of csv,dkvp,nidx,pprint,xtab}
      --irs {record-separator character}
      --ifs {field-separator character}
      --ips {pair-separator character}
      --repifs
      --repips
      --mmap
      --no-mmap
    Please use "mlr --usage-separator-options" for information on specifying separators.
    Please see http://johnkerl.org/miller/doc/reference.html for more information
    including examples.

  label
    Usage: mlr label {new1,new2,new3,...}
    Given n comma-separated names, renames the first n fields of each record to
    have the respective name. (Fields past the nth are left with their original
    names.) Particularly useful with --inidx or --implicit-csv-header, to give
    useful names to otherwise integer-indexed fields.
    Examples:
      "echo 'a b c d' | mlr --inidx --odkvp cat"       gives "1=a,2=b,3=c,4=d"
      "echo 'a b c d' | mlr --inidx --odkvp label s,t" gives "s=a,t=b,3=c,4=d"

  least-frequent
    Usage: mlr least-frequent [options]
    Shows the least frequently occurring distinct values for specified field names.
    The first entry is the statistical anti-mode; the remaining are runners-up.
    Options:
    -f {one or more comma-separated field names}. Required flag.
    -n {count}. Optional flag defaulting to 10.
    -b          Suppress counts; show only field values.
    -o {name}   Field name for output count. Default "count".
    See also "mlr most-frequent".

  merge-fields
    Usage: mlr merge-fields [options]
    Computes univariate statistics for each input record, accumulated across
    specified fields.
    Options:
    -a {sum,count,...}  Names of accumulators. One or more of:
      count     Count instances of fields
      mode      Find most-frequently-occurring values for fields; first-found wins tie
      antimode  Find least-frequently-occurring values for fields; first-found wins tie
      sum       Compute sums of specified fields
      mean      Compute averages (sample means) of specified fields
      stddev    Compute sample standard deviation of specified fields
      var       Compute sample variance of specified fields
      meaneb    Estimate error bars for averages (assuming no sample autocorrelation)
      skewness  Compute sample skewness of specified fields
      kurtosis  Compute sample kurtosis of specified fields
      min       Compute minimum values of specified fields
      max       Compute maximum values of specified fields
    -f {a,b,c}  Value-field names on which to compute statistics. Requires -o.
    -r {a,b,c}  Regular expressions for value-field names on which to compute
                statistics. Requires -o.
    -c {a,b,c}  Substrings for collapse mode. All fields which have the same names
                after removing substrings will be accumulated together. Please see
                examples below.
    -i          Use interpolated percentiles, like R's type=7; default like type=1.
                Not sensical for string-valued fields.
    -o {name}   Output field basename for -f/-r.
    -k          Keep the input fields which contributed to the output statistics;
                the default is to omit them.
    -F          Computes integerable things (e.g. count) in floating point.
    String-valued data make sense unless arithmetic on them is required,
    e.g. for sum, mean, interpolated percentiles, etc. In case of mixed data,
    numbers are less than strings.
    Example input data: "a_in_x=1,a_out_x=2,b_in_y=4,b_out_x=8".
    Example: mlr merge-fields -a sum,count -f a_in_x,a_out_x -o foo
      produces "b_in_y=4,b_out_x=8,foo_sum=3,foo_count=2" since "a_in_x,a_out_x" are
      summed over.
    Example: mlr merge-fields -a sum,count -r in_,out_ -o bar
      produces "bar_sum=15,bar_count=4" since all four fields are summed over.
    Example: mlr merge-fields -a sum,count -c in_,out_
      produces "a_x_sum=3,a_x_count=2,b_y_sum=4,b_y_count=1,b_x_sum=8,b_x_count=1"
      since "a_in_x" and "a_out_x" both collapse to "a_x", "b_in_y" collapses to
      "b_y", and "b_out_x" collapses to "b_x".

  most-frequent
    Usage: mlr most-frequent [options]
    Shows the most frequently occurring distinct values for specified field names.
    The first entry is the statistical mode; the remaining are runners-up.
    Options:
    -f {one or more comma-separated field names}. Required flag.
    -n {count}. Optional flag defaulting to 10.
    -b          Suppress counts; show only field values.
    -o {name}   Field name for output count. Default "count".
    See also "mlr least-frequent".

  nest
    Usage: mlr nest [options]
    Explodes specified field values into separate fields/records, or reverses this.
    Options:
      --explode,--implode   One is required.
      --values,--pairs      One is required.
      --across-records,--across-fields One is required.
      -f {field name}       Required.
      --nested-fs {string}  Defaults to ";". Field separator for nested values.
      --nested-ps {string}  Defaults to ":". Pair separator for nested key-value pairs.
      --evar {string}       Shorthand for --explode --values ---across-records --nested-fs {string}
    Please use "mlr --usage-separator-options" for information on specifying separators.
    Examples:
      mlr nest --explode --values --across-records -f x
      with input record "x=a;b;c,y=d" produces output records
        "x=a,y=d"
        "x=b,y=d"
        "x=c,y=d"
      Use --implode to do the reverse.
      mlr nest --explode --values --across-fields -f x
      with input record "x=a;b;c,y=d" produces output records
        "x_1=a,x_2=b,x_3=c,y=d"
      Use --implode to do the reverse.
      mlr nest --explode --pairs --across-records -f x
      with input record "x=a:1;b:2;c:3,y=d" produces output records
        "a=1,y=d"
        "b=2,y=d"
        "c=3,y=d"
      mlr nest --explode --pairs --across-fields -f x
      with input record "x=a:1;b:2;c:3,y=d" produces output records
        "a=1,b=2,c=3,y=d"
    Notes:
    * With --pairs, --implode doesn't make sense since the original field name has
      been lost.
    * The combination "--implode --values --across-records" is non-streaming:
      no output records are produced until all input records have been read. In
      particular, this means it won't work in tail -f contexts. But all other flag
      combinations result in streaming (tail -f friendly) data processing.
    * It's up to you to ensure that the nested-fs is distinct from your data's IFS:
      e.g. by default the former is semicolon and the latter is comma.
    See also mlr reshape.

  nothing
    Usage: mlr nothing [options]
    Drops all input records. Useful for testing, or after tee/print/etc. have
    produced other output.

  put
    Usage: mlr put [options] {expression}
    Adds/updates specified field(s). Expressions are semicolon-separated and must
    either be assignments, or evaluate to boolean.  Booleans with following
    statements in curly braces control whether those statements are executed;
    booleans without following curly braces do nothing except side effects (e.g.
    regex-captures into \1, \2, etc.).
    Conversion options:
    -S: Keeps field values as strings with no type inference to int or float.
    -F: Keeps field values as strings or floats with no inference to int.
    All field values are type-inferred to int/float/string unless this behavior is
    suppressed with -S or -F.
    Output/formatting options:
    --oflatsep {string}: Separator to use when flattening multi-level @-variables
        to output records for emit. Default ":".
    --jknquoteint: For dump output (JSON-formatted), do not quote map keys if non-string.
    --jvquoteall: For dump output (JSON-formatted), quote map values even if non-string.
    Any of the output-format command-line flags (see mlr -h). Example: using
      mlr --icsv --opprint ... then put --ojson 'tee > "mytap-".$a.".dat", $*' then ...
    the input is CSV, the output is pretty-print tabular, but the tee-file output
    is written in JSON format.
    --no-fflush: for emit, tee, print, and dump, don't call fflush() after every
        record.
    Expression-specification options:
    -f {filename}: the DSL expression is taken from the specified file rather
        than from the command line. Outer single quotes wrapping the expression
        should not be placed in the file. If -f is specified more than once,
        all input files specified using -f are concatenated to produce the expression.
        (For example, you can define functions in one file and call them from another.)
    -e {expression}: You can use this after -f to add an expression. Example use
        case: define functions/subroutines in a file you specify with -f, then call
        them with an expression you specify with -e.
    (If you mix -e and -f then the expressions are evaluated in the order encountered.
    Since the expression pieces are simply concatenated, please be sure to use intervening
    semicolons to separate expressions.)
    Tracing options:
    -v: Prints the expressions's AST (abstract syntax tree), which gives
        full transparency on the precedence and associativity rules of
        Miller's grammar, to stdout.
    -a: Prints a low-level stack-allocation trace to stdout.
    -t: Prints a low-level parser trace to stderr.
    -T: Prints a every statement to stderr as it is executed.
    Other options:
    -q: Does not include the modified record in the output stream. Useful for when
        all desired output is in begin and/or end blocks.
    Please use a dollar sign for field names and double-quotes for string
    literals. If field names have special characters such as "." then you might
    use braces, e.g. '${field.name}'. Miller built-in variables are
    NF NR FNR FILENUM FILENAME M_PI M_E, and ENV["namegoeshere"] to access environment
    variables. The environment-variable name may be an expression, e.g. a field
    value.
    Use # to comment to end of line.
    Examples:
      mlr put '$y = log10($x); $z = sqrt($y)'
      mlr put '$x>0.0 { $y=log10($x); $z=sqrt($y) }' # does {...} only if $x > 0.0
      mlr put '$x>0.0;  $y=log10($x); $z=sqrt($y)'   # does all three statements
      mlr put '$a =~ "([a-z]+)_([0-9]+);  $b = "left_\1"; $c = "right_\2"'
      mlr put '$a =~ "([a-z]+)_([0-9]+) { $b = "left_\1"; $c = "right_\2" }'
      mlr put '$filename = FILENAME'
      mlr put '$colored_shape = $color . "_" . $shape'
      mlr put '$y = cos($theta); $z = atan2($y, $x)'
      mlr put '$name = sub($name, "http.*com"i, "")'
      mlr put -q '@sum += $x; end {emit @sum}'
      mlr put -q '@sum[$a] += $x; end {emit @sum, "a"}'
      mlr put -q '@sum[$a][$b] += $x; end {emit @sum, "a", "b"}'
      mlr put -q '@min=min(@min,$x);@max=max(@max,$x); end{emitf @min, @max}'
      mlr put -q 'is_null(@xmax) || $x > @xmax {@xmax=$x; @recmax=$*}; end {emit @recmax}'
      mlr put '
        $x = 1;
       #$y = 2;
        $z = 3
      '
    Please see also 'mlr -k' for examples using redirected output.
    Please see http://johnkerl.org/miller/doc/reference.html for more information
    including function list. Or "mlr -f".
    Please see in particular:
      http://www.johnkerl.org/miller/doc/reference.html#put

  regularize
    Usage: mlr regularize
    For records seen earlier in the data stream with same field names in
    a different order, outputs them with field names in the previously
    encountered order.
    Example: input records a=1,c=2,b=3, then e=4,d=5, then c=7,a=6,b=8
    output as              a=1,c=2,b=3, then e=4,d=5, then a=6,c=7,b=8

  rename
    Usage: mlr rename [options] {old1,new1,old2,new2,...}
    Renames specified fields.
    Options:
    -r         Treat old field  names as regular expressions. "ab", "a.*b"
               will match any field name containing the substring "ab" or
               matching "a.*b", respectively; anchors of the form "^ab$",
               "^a.*b$" may be used. New field names may be plain strings,
               or may contain capture groups of the form "\1" through
               "\9". Wrapping the regex in double quotes is optional, but
               is required if you wish to follow it with 'i' to indicate
               case-insensitivity.
    -g         Do global replacement within each field name rather than
               first-match replacement.
    Examples:
    mlr rename old_name,new_name'
    mlr rename old_name_1,new_name_1,old_name_2,new_name_2'
    mlr rename -r 'Date_[0-9]+,Date,'  Rename all such fields to be "Date"
    mlr rename -r '"Date_[0-9]+",Date' Same
    mlr rename -r 'Date_([0-9]+).*,\1' Rename all such fields to be of the form 20151015
    mlr rename -r '"name"i,Name'       Rename "name", "Name", "NAME", etc. to "Name"

  reorder
    Usage: mlr reorder [options]
    -f {a,b,c}   Field names to reorder.
    -e           Put specified field names at record end: default is to put
                 them at record start.
    Examples:
    mlr reorder    -f a,b sends input record "d=4,b=2,a=1,c=3" to "a=1,b=2,d=4,c=3".
    mlr reorder -e -f a,b sends input record "d=4,b=2,a=1,c=3" to "d=4,c=3,a=1,b=2".

  repeat
    Usage: mlr repeat [options]
    Copies input records to output records multiple times.
    Options must be exactly one of the following:
      -n {repeat count}  Repeat each input record this many times.
      -f {field name}    Same, but take the repeat count from the specified
                         field name of each input record.
    Example:
      echo x=0 | mlr repeat -n 4 then put '$x=urand()'
    produces:
     x=0.488189
     x=0.484973
     x=0.704983
     x=0.147311
    Example:
      echo a=1,b=2,c=3 | mlr repeat -f b
    produces:
      a=1,b=2,c=3
      a=1,b=2,c=3
    Example:
      echo a=1,b=2,c=3 | mlr repeat -f c
    produces:
      a=1,b=2,c=3
      a=1,b=2,c=3
      a=1,b=2,c=3

  reshape
    Usage: mlr reshape [options]
    Wide-to-long options:
      -i {input field names}   -o {key-field name,value-field name}
      -r {input field regexes} -o {key-field name,value-field name}
      These pivot/reshape the input data such that the input fields are removed
      and separate records are emitted for each key/value pair.
      Note: this works with tail -f and produces output records for each input
      record seen.
    Long-to-wide options:
      -s {key-field name,value-field name}
      These pivot/reshape the input data to undo the wide-to-long operation.
      Note: this does not work with tail -f; it produces output records only after
      all input records have been read.
    Examples:
      Input file "wide.txt":
        time       X           Y
        2009-01-01 0.65473572  2.4520609
        2009-01-02 -0.89248112 0.2154713
        2009-01-03 0.98012375  1.3179287
      mlr --pprint reshape -i X,Y -o item,value wide.txt
        time       item value
        2009-01-01 X    0.65473572
        2009-01-01 Y    2.4520609
        2009-01-02 X    -0.89248112
        2009-01-02 Y    0.2154713
        2009-01-03 X    0.98012375
        2009-01-03 Y    1.3179287
      mlr --pprint reshape -r '[A-Z]' -o item,value wide.txt
        time       item value
        2009-01-01 X    0.65473572
        2009-01-01 Y    2.4520609
        2009-01-02 X    -0.89248112
        2009-01-02 Y    0.2154713
        2009-01-03 X    0.98012375
        2009-01-03 Y    1.3179287
      Input file "long.txt":
        time       item value
        2009-01-01 X    0.65473572
        2009-01-01 Y    2.4520609
        2009-01-02 X    -0.89248112
        2009-01-02 Y    0.2154713
        2009-01-03 X    0.98012375
        2009-01-03 Y    1.3179287
      mlr --pprint reshape -s item,value long.txt
        time       X           Y
        2009-01-01 0.65473572  2.4520609
        2009-01-02 -0.89248112 0.2154713
        2009-01-03 0.98012375  1.3179287
    See also mlr nest.

  sample
    Usage: mlr sample [options]
    Reservoir sampling (subsampling without replacement), optionally by category.
    -k {count}    Required: number of records to output, total, or by group if using -g.
    -g {a,b,c}    Optional: group-by-field names for samples.
    See also mlr bootstrap and mlr shuffle.

  sec2gmt
    Usage: mlr sec2gmt [options] {comma-separated list of field names}
    Replaces a numeric field representing seconds since the epoch with the
    corresponding GMT timestamp; leaves non-numbers as-is. This is nothing
    more than a keystroke-saver for the sec2gmt function:
      mlr sec2gmt time1,time2
    is the same as
      mlr put '$time1=sec2gmt($time1);$time2=sec2gmt($time2)'
    Options:
    -1 through -9: format the seconds using 1..9 decimal places, respectively.

  sec2gmtdate
    Usage: mlr sec2gmtdate {comma-separated list of field names}
    Replaces a numeric field representing seconds since the epoch with the
    corresponding GMT year-month-day timestamp; leaves non-numbers as-is.
    This is nothing more than a keystroke-saver for the sec2gmtdate function:
      mlr sec2gmtdate time1,time2
    is the same as
      mlr put '$time1=sec2gmtdate($time1);$time2=sec2gmtdate($time2)'

  seqgen
    Usage: mlr seqgen [options]
    Produces a sequence of counters.  Discards the input record stream. Produces
    output as specified by the following options:
    -f {name} Field name for counters; default "i".
    --start {number} Inclusive start value; default "1".
    --stop  {number} Inclusive stop value; default "100".
    --step  {number} Step value; default "1".
    Start, stop, and/or step may be floating-point. Output is integer if start,
    stop, and step are all integers. Step may be negative. It may not be zero
    unless start == stop.

  shuffle
    Usage: mlr shuffle {no options}
    Outputs records randomly permuted. No output records are produced until
    all input records are read.
    See also mlr bootstrap and mlr sample.

  sort
    Usage: mlr sort {flags}
    Flags:
      -f  {comma-separated field names}  Lexical ascending
      -n  {comma-separated field names}  Numerical ascending; nulls sort last
      -nf {comma-separated field names}  Numerical ascending; nulls sort last
      -r  {comma-separated field names}  Lexical descending
      -nr {comma-separated field names}  Numerical descending; nulls sort first
    Sorts records primarily by the first specified field, secondarily by the second
    field, and so on.  (Any records not having all specified sort keys will appear
    at the end of the output, in the order they were encountered, regardless of the
    specified sort order.) The sort is stable: records that compare equal will sort
    in the order they were encountered in the input record stream.
    Example:
      mlr sort -f a,b -nr x,y,z
    which is the same as:
      mlr sort -f a -f b -nr x -nr y -nr z

  stats1
    Usage: mlr stats1 [options]
    Computes univariate statistics for one or more given fields, accumulated across
    the input record stream.
    Options:
    -a {sum,count,...}  Names of accumulators: p10 p25.2 p50 p98 p100 etc. and/or
                        one or more of:
       count     Count instances of fields
       mode      Find most-frequently-occurring values for fields; first-found wins tie
       antimode  Find least-frequently-occurring values for fields; first-found wins tie
       sum       Compute sums of specified fields
       mean      Compute averages (sample means) of specified fields
       stddev    Compute sample standard deviation of specified fields
       var       Compute sample variance of specified fields
       meaneb    Estimate error bars for averages (assuming no sample autocorrelation)
       skewness  Compute sample skewness of specified fields
       kurtosis  Compute sample kurtosis of specified fields
       min       Compute minimum values of specified fields
       max       Compute maximum values of specified fields
    -f {a,b,c}   Value-field names on which to compute statistics
    --fr {regex} Regex for value-field names on which to compute statistics
                 (compute statsitics on values in all field names matching regex)
    --fx {regex} Inverted regex for value-field names on which to compute statistics
                 (compute statsitics on values in all field names not matching regex)
    -g {d,e,f}   Optional group-by-field names
    --gr {regex} Regex for optional group-by-field names
                 (group by values in field names matching regex)
    --gx {regex} Inverted regex for optional group-by-field names
                 (group by values in field names not matching regex)
    --grfx {regex} Shorthand for --gr {regex} --fx {that same regex}
    -i           Use interpolated percentiles, like R's type=7; default like type=1.
                 Not sensical for string-valued fields.
    -s           Print iterative stats. Useful in tail -f contexts (in which
                 case please avoid pprint-format output since end of input
                 stream will never be seen).
    -F           Computes integerable things (e.g. count) in floating point.
    Example: mlr stats1 -a min,p10,p50,p90,max -f value -g size,shape
    Example: mlr stats1 -a count,mode -f size
    Example: mlr stats1 -a count,mode -f size -g shape
    Example: mlr stats1 -a count,mode --fr '^[a-h].*$' -gr '^k.*$'
             This computes count and mode statistics on all field names beginning
             with a through h, grouped by all field names starting with k.
    Notes:
    * p50 and median are synonymous.
    * min and max output the same results as p0 and p100, respectively, but use
      less memory.
    * String-valued data make sense unless arithmetic on them is required,
      e.g. for sum, mean, interpolated percentiles, etc. In case of mixed data,
      numbers are less than strings.
    * count and mode allow text input; the rest require numeric input.
      In particular, 1 and 1.0 are distinct text for count and mode.
    * When there are mode ties, the first-encountered datum wins.

  stats2
    Usage: mlr stats2 [options]
    Computes bivariate statistics for one or more given field-name pairs,
    accumulated across the input record stream.
    -a {linreg-ols,corr,...}  Names of accumulators: one or more of:
      linreg-pca   Linear regression using principal component analysis
      linreg-ols   Linear regression using ordinary least squares
      r2           Quality metric for linreg-ols (linreg-pca emits its own)
      logireg      Logistic regression
      corr         Sample correlation
      cov          Sample covariance
      covx         Sample-covariance matrix
    -f {a,b,c,d}   Value-field name-pairs on which to compute statistics.
                   There must be an even number of names.
    -g {e,f,g}     Optional group-by-field names.
    -v             Print additional output for linreg-pca.
    -s             Print iterative stats. Useful in tail -f contexts (in which
                   case please avoid pprint-format output since end of input
                   stream will never be seen).
    --fit          Rather than printing regression parameters, applies them to
                   the input data to compute new fit fields. All input records are
                   held in memory until end of input stream. Has effect only for
                   linreg-ols, linreg-pca, and logireg.
    Only one of -s or --fit may be used.
    Example: mlr stats2 -a linreg-pca -f x,y
    Example: mlr stats2 -a linreg-ols,r2 -f x,y -g size,shape
    Example: mlr stats2 -a corr -f x,y

  step
    Usage: mlr step [options]
    Computes values dependent on the previous record, optionally grouped
    by category.
    Options:
    -a {delta,rsum,...}   Names of steppers: comma-separated, one or more of:
      delta    Compute differences in field(s) between successive records
      shift    Include value(s) in field(s) from previous record, if any
      from-first Compute differences in field(s) from first record
      ratio    Compute ratios in field(s) between successive records
      rsum     Compute running sums of field(s) between successive records
      counter  Count instances of field(s) between successive records
      ewma     Exponentially weighted moving average over successive records
    -f {a,b,c} Value-field names on which to compute statistics
    -g {d,e,f} Optional group-by-field names
    -F         Computes integerable things (e.g. counter) in floating point.
    -d {x,y,z} Weights for ewma. 1 means current sample gets all weight (no
               smoothing), near under under 1 is light smoothing, near over 0 is
               heavy smoothing. Multiple weights may be specified, e.g.
               "mlr step -a ewma -f sys_load -d 0.01,0.1,0.9". Default if omitted
               is "-d 0.5".
    -o {a,b,c} Custom suffixes for EWMA output fields. If omitted, these default to
               the -d values. If supplied, the number of -o values must be the same
               as the number of -d values.
    Examples:
      mlr step -a rsum -f request_size
      mlr step -a delta -f request_size -g hostname
      mlr step -a ewma -d 0.1,0.9 -f x,y
      mlr step -a ewma -d 0.1,0.9 -o smooth,rough -f x,y
      mlr step -a ewma -d 0.1,0.9 -o smooth,rough -f x,y -g group_name
    Please see http://johnkerl.org/miller/doc/reference.html#filter or
    https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
    for more information on EWMA.

  tac
    Usage: mlr tac
    Prints records in reverse order from the order in which they were encountered.

  tail
    Usage: mlr tail [options]
    -n {count}    Tail count to print; default 10
    -g {a,b,c}    Optional group-by-field names for tail counts
    Passes through the last n records, optionally by category.

  tee
    Usage: mlr tee [options] {filename}
    Passes through input records (like mlr cat) but also writes to specified output
    file, using output-format flags from the command line (e.g. --ocsv). See also
    the "tee" keyword within mlr put, which allows data-dependent filenames.
    Options:
    -a:          append to existing file, if any, rather than overwriting.
    --no-fflush: don't call fflush() after every record.
    Any of the output-format command-line flags (see mlr -h). Example: using
      mlr --icsv --opprint put '...' then tee --ojson ./mytap.dat then stats1 ...
    the input is CSV, the output is pretty-print tabular, but the tee-file output
    is written in JSON format.

  top
    Usage: mlr top [options]
    -f {a,b,c}    Value-field names for top counts.
    -g {d,e,f}    Optional group-by-field names for top counts.
    -n {count}    How many records to print per category; default 1.
    -a            Print all fields for top-value records; default is
                  to print only value and group-by fields. Requires a single
                  value-field name only.
    --min         Print top smallest values; default is top largest values.
    -F            Keep top values as floats even if they look like integers.
    -o {name}     Field name for output indices. Default "top_idx".
    Prints the n records with smallest/largest values at specified fields,
    optionally by category.

  uniq
    Usage: mlr uniq [options]
    -g {d,e,f}    Group-by-field names for uniq counts.
    -c            Show repeat counts in addition to unique values.
    -n            Show only the number of distinct values.
    -o {name}     Field name for output count. Default "count".
    Prints distinct values for specified field names. With -c, same as
    count-distinct. For uniq, -f is a synonym for -g.

  unsparsify
    Usage: mlr unsparsify [options]
    Prints records with the union of field names over all input records.
    For field names absent in a given record but present in others, fills in
    a value. This verb retains all input before producing any output.
    Options:
    --fill-with {filler string}  What to fill absent fields with. Defaults to
                                 the empty string.
    Example: if the input is two records, one being 'a=1,b=2' and the other
    being 'b=3,c=4', then the output is the two records 'a=1,b=2,c=' and

FUNCTIONS FOR FILTER/PUT

  +
    (class=arithmetic #args=2): Addition.
    + (class=arithmetic #args=1): Unary plus.

  -
    (class=arithmetic #args=2): Subtraction.
    - (class=arithmetic #args=1): Unary minus.

  *
    (class=arithmetic #args=2): Multiplication.

  /
    (class=arithmetic #args=2): Division.

  //
    (class=arithmetic #args=2): Integer division: rounds to negative (pythonic).

  .+
    (class=arithmetic #args=2): Addition, with integer-to-integer overflow
    .+ (class=arithmetic #args=1): Unary plus, with integer-to-integer overflow.

  .-
    (class=arithmetic #args=2): Subtraction, with integer-to-integer overflow.
    .- (class=arithmetic #args=1): Unary minus, with integer-to-integer overflow.

  .*
    (class=arithmetic #args=2): Multiplication, with integer-to-integer overflow.

  ./
    (class=arithmetic #args=2): Division, with integer-to-integer overflow.

  .//
    (class=arithmetic #args=2): Integer division: rounds to negative (pythonic), with integer-to-integer overflow.

  %
    (class=arithmetic #args=2): Remainder; never negative-valued (pythonic).

  **
    (class=arithmetic #args=2): Exponentiation; same as pow, but as an infix
    operator.

  |
    (class=arithmetic #args=2): Bitwise OR.

  ^
    (class=arithmetic #args=2): Bitwise XOR.

  &
    (class=arithmetic #args=2): Bitwise AND.

  ~
    (class=arithmetic #args=1): Bitwise NOT. Beware '$y=~$x' since =~ is the
    regex-match operator: try '$y = ~$x'.

  <<
    (class=arithmetic #args=2): Bitwise left-shift.

  >>
    (class=arithmetic #args=2): Bitwise right-shift.

  bitcount
    (class=arithmetic #args=1): Count of 1-bits

  ==
    (class=boolean #args=2): String/numeric equality. Mixing number and string
    results in string compare.

  !=
    (class=boolean #args=2): String/numeric inequality. Mixing number and string
    results in string compare.

  =~
    (class=boolean #args=2): String (left-hand side) matches regex (right-hand
    side), e.g. '$name =~ "^a.*b$"'.

  !=~
    (class=boolean #args=2): String (left-hand side) does not match regex
    (right-hand side), e.g. '$name !=~ "^a.*b$"'.

  >
    (class=boolean #args=2): String/numeric greater-than. Mixing number and string
    results in string compare.

  >=
    (class=boolean #args=2): String/numeric greater-than-or-equals. Mixing number
    and string results in string compare.

  <
    (class=boolean #args=2): String/numeric less-than. Mixing number and string
    results in string compare.

  <=
    (class=boolean #args=2): String/numeric less-than-or-equals. Mixing number
    and string results in string compare.

  &&
    (class=boolean #args=2): Logical AND.

  ||
    (class=boolean #args=2): Logical OR.

  ^^
    (class=boolean #args=2): Logical XOR.

  !
    (class=boolean #args=1): Logical negation.

  ? :
    (class=boolean #args=3): Ternary operator.

  .
    (class=string #args=2): String concatenation.

  gsub
    (class=string #args=3): Example: '$name=gsub($name, "old", "new")'
    (replace all).

  strlen
    (class=string #args=1): String length.

  sub
    (class=string #args=3): Example: '$name=sub($name, "old", "new")'
    (replace once).

  substr
    (class=string #args=3): substr(s,m,n) gives substring of s from 0-up position m to n
    inclusive. Negative indices -len .. -1 alias to 0 .. len-1.

  tolower
    (class=string #args=1): Convert string to lowercase.

  toupper
    (class=string #args=1): Convert string to uppercase.

  abs
    (class=math #args=1): Absolute value.

  acos
    (class=math #args=1): Inverse trigonometric cosine.

  acosh
    (class=math #args=1): Inverse hyperbolic cosine.

  asin
    (class=math #args=1): Inverse trigonometric sine.

  asinh
    (class=math #args=1): Inverse hyperbolic sine.

  atan
    (class=math #args=1): One-argument arctangent.

  atan2
    (class=math #args=2): Two-argument arctangent.

  atanh
    (class=math #args=1): Inverse hyperbolic tangent.

  cbrt
    (class=math #args=1): Cube root.

  ceil
    (class=math #args=1): Ceiling: nearest integer at or above.

  cos
    (class=math #args=1): Trigonometric cosine.

  cosh
    (class=math #args=1): Hyperbolic cosine.

  erf
    (class=math #args=1): Error function.

  erfc
    (class=math #args=1): Complementary error function.

  exp
    (class=math #args=1): Exponential function e**x.

  expm1
    (class=math #args=1): e**x - 1.

  floor
    (class=math #args=1): Floor: nearest integer at or below.

  invqnorm
    (class=math #args=1): Inverse of normal cumulative distribution
    function. Note that invqorm(urand()) is normally distributed.

  log
    (class=math #args=1): Natural (base-e) logarithm.

  log10
    (class=math #args=1): Base-10 logarithm.

  log1p
    (class=math #args=1): log(1-x).

  logifit
    (class=math #args=3): Given m and b from logistic regression, compute
    fit: $yhat=logifit($x,$m,$b).

  madd
    (class=math #args=3): a + b mod m (integers)

  max
    (class=math variadic): max of n numbers; null loses

  mexp
    (class=math #args=3): a ** b mod m (integers)

  min
    (class=math variadic): Min of n numbers; null loses

  mmul
    (class=math #args=3): a * b mod m (integers)

  msub
    (class=math #args=3): a - b mod m (integers)

  pow
    (class=math #args=2): Exponentiation; same as **.

  qnorm
    (class=math #args=1): Normal cumulative distribution function.

  round
    (class=math #args=1): Round to nearest integer.

  roundm
    (class=math #args=2): Round to nearest multiple of m: roundm($x,$m) is
    the same as round($x/$m)*$m

  sgn
    (class=math #args=1): +1 for positive input, 0 for zero input, -1 for
    negative input.

  sin
    (class=math #args=1): Trigonometric sine.

  sinh
    (class=math #args=1): Hyperbolic sine.

  sqrt
    (class=math #args=1): Square root.

  tan
    (class=math #args=1): Trigonometric tangent.

  tanh
    (class=math #args=1): Hyperbolic tangent.

  urand
    (class=math #args=0): Floating-point numbers on the unit interval.
    Int-valued example: '$n=floor(20+urand()*11)'.

  urand32
    (class=math #args=0): Integer uniformly distributed 0 and 2**32-1
    inclusive.

  urandint
    (class=math #args=2): Integer uniformly distributed between inclusive
    integer endpoints.

  dhms2fsec
    (class=time #args=1): Recovers floating-point seconds as in
    dhms2fsec("5d18h53m20.250000s") = 500000.250000

  dhms2sec
    (class=time #args=1): Recovers integer seconds as in
    dhms2sec("5d18h53m20s") = 500000

  fsec2dhms
    (class=time #args=1): Formats floating-point seconds as in
    fsec2dhms(500000.25) = "5d18h53m20.250000s"

  fsec2hms
    (class=time #args=1): Formats floating-point seconds as in
    fsec2hms(5000.25) = "01:23:20.250000"

  gmt2sec
    (class=time #args=1): Parses GMT timestamp as integer seconds since
    the epoch.

  hms2fsec
    (class=time #args=1): Recovers floating-point seconds as in
    hms2fsec("01:23:20.250000") = 5000.250000

  hms2sec
    (class=time #args=1): Recovers integer seconds as in
    hms2sec("01:23:20") = 5000

  sec2dhms
    (class=time #args=1): Formats integer seconds as in sec2dhms(500000)
    = "5d18h53m20s"

  sec2gmt
    (class=time #args=1): Formats seconds since epoch (integer part)
    as GMT timestamp, e.g. sec2gmt(1440768801.7) = "2015-08-28T13:33:21Z".
    Leaves non-numbers as-is.
    sec2gmt (class=time #args=2): Formats seconds since epoch as GMT timestamp with n
    decimal places for seconds, e.g. sec2gmt(1440768801.7,1) = "2015-08-28T13:33:21.7Z".
    Leaves non-numbers as-is.

  sec2gmtdate
    (class=time #args=1): Formats seconds since epoch (integer part)
    as GMT timestamp with year-month-date, e.g. sec2gmtdate(1440768801.7) = "2015-08-28".
    Leaves non-numbers as-is.

  sec2hms
    (class=time #args=1): Formats integer seconds as in
    sec2hms(5000) = "01:23:20"

  strftime
    (class=time #args=2): Formats seconds since the epoch as timestamp, e.g.
    strftime(1440768801.7,"%Y-%m-%dT%H:%M:%SZ") = "2015-08-28T13:33:21Z", and
    strftime(1440768801.7,"%Y-%m-%dT%H:%M:%3SZ") = "2015-08-28T13:33:21.700Z".
    Format strings are as in the C library (please see "man strftime" on your system),
    with the Miller-specific addition of "%1S" through "%9S" which format the seocnds
    with 1 through 9 decimal places, respectively. ("%S" uses no decimal places.)

  strptime
    (class=time #args=2): Parses timestamp as floating-point seconds since the epoch,
    e.g. strptime("2015-08-28T13:33:21Z","%Y-%m-%dT%H:%M:%SZ") = 1440768801.000000,
    and  strptime("2015-08-28T13:33:21.345Z","%Y-%m-%dT%H:%M:%SZ") = 1440768801.345000.

  systime
    (class=time #args=0): Floating-point seconds since the epoch,
    e.g. 1440768801.748936.

  is_absent
    (class=typing #args=1): False if field is present in input, false otherwise

  is_bool
    (class=typing #args=1): True if field is present with boolean value. Synonymous with is_boolean.

  is_boolean
    (class=typing #args=1): True if field is present with boolean value. Synonymous with is_bool.

  is_empty
    (class=typing #args=1): True if field is present in input with empty string value, false otherwise.

  is_empty_map
    (class=typing #args=1): True if argument is a map which is empty.

  is_float
    (class=typing #args=1): True if field is present with value inferred to be float

  is_int
    (class=typing #args=1): True if field is present with value inferred to be int

  is_map
    (class=typing #args=1): True if argument is a map.

  is_nonempty_map
    (class=typing #args=1): True if argument is a map which is non-empty.

  is_not_empty
    (class=typing #args=1): False if field is present in input with empty value, false otherwise

  is_not_map
    (class=typing #args=1): True if argument is not a map.

  is_not_null
    (class=typing #args=1): False if argument is null (empty or absent), true otherwise.

  is_null
    (class=typing #args=1): True if argument is null (empty or absent), false otherwise.

  is_numeric
    (class=typing #args=1): True if field is present with value inferred to be int or float

  is_present
    (class=typing #args=1): True if field is present in input, false otherwise.

  is_string
    (class=typing #args=1): True if field is present with string (including empty-string) value

  asserting_absent
    (class=typing #args=1): Returns argument if it is absent in the input data, else
    throws an error.

  asserting_bool
    (class=typing #args=1): Returns argument if it is present with boolean value, else
    throws an error.

  asserting_boolean
    (class=typing #args=1): Returns argument if it is present with boolean value, else
    throws an error.

  asserting_empty
    (class=typing #args=1): Returns argument if it is present in input with empty value,
    else throws an error.

  asserting_empty_map
    (class=typing #args=1): Returns argument if it is a map with empty value, else
    throws an error.

  asserting_float
    (class=typing #args=1): Returns argument if it is present with float value, else
    throws an error.

  asserting_int
    (class=typing #args=1): Returns argument if it is present with int value, else
    throws an error.

  asserting_map
    (class=typing #args=1): Returns argument if it is a map, else throws an error.

  asserting_nonempty_map
    (class=typing #args=1): Returns argument if it is a non-empty map, else throws
    an error.

  asserting_not_empty
    (class=typing #args=1): Returns argument if it is present in input with non-empty
    value, else throws an error.

  asserting_not_map
    (class=typing #args=1): Returns argument if it is not a map, else throws an error.

  asserting_not_null
    (class=typing #args=1): Returns argument if it is non-null (non-empty and non-absent),
    else throws an error.

  asserting_null
    (class=typing #args=1): Returns argument if it is null (empty or absent), else throws
    an error.

  asserting_numeric
    (class=typing #args=1): Returns argument if it is present with int or float value,
    else throws an error.

  asserting_present
    (class=typing #args=1): Returns argument if it is present in input, else throws
    an error.

  asserting_string
    (class=typing #args=1): Returns argument if it is present with string (including
    empty-string) value, else throws an error.

  boolean
    (class=conversion #args=1): Convert int/float/bool/string to boolean.

  float
    (class=conversion #args=1): Convert int/float/bool/string to float.

  fmtnum
    (class=conversion #args=2): Convert int/float/bool to string using
    printf-style format string, e.g. '$s = fmtnum($n, "%06lld")'. WARNING: Miller numbers
    are all long long or double. If you use formats like %d or %f, behavior is undefined.

  hexfmt
    (class=conversion #args=1): Convert int to string, e.g. 255 to "0xff".

  int
    (class=conversion #args=1): Convert int/float/bool/string to int.

  string
    (class=conversion #args=1): Convert int/float/bool/string to string.

  typeof
    (class=conversion #args=1): Convert argument to type of argument (e.g.
    MT_STRING). For debug.

  depth
    (class=maps #args=1): Prints maximum depth of hashmap: ''. Scalars have depth 0.

  haskey
    (class=maps #args=2): True/false if map has/hasn't key, e.g. 'haskey($*, "a")' or

  joink
    (class=maps #args=2): Makes string from map keys. E.g. 'joink($*, ",")'.

  joinkv
    (class=maps #args=3): Makes string from map key-value pairs. E.g. 'joinkv(@v[2], "=", ",")'

  joinv
    (class=maps #args=2): Makes string from map keys. E.g. 'joinv(mymap, ",")'.

  leafcount
    (class=maps #args=1): Counts total number of terminal values in hashmap. For single-level maps,
    same as length.

  length
    (class=maps #args=1): Counts number of top-level entries in hashmap. Scalars have length 1.

  mapdiff
    (class=maps variadic): With 0 args, returns empty map. With 1 arg, returns copy of arg.
    With 2 or more, returns copy of arg 1 with all keys from any of remaining argument maps removed.

  mapexcept
    (class=maps variadic): Returns a map with keys from remaining arguments, if any, unset.
    E.g. 'mapexcept({1:2,3:4,5:6}, 1, 5, 7)' is '{3:4}'.

  mapselect
    (class=maps variadic): Returns a map with only keys from remaining arguments set.
    E.g. 'mapselect({1:2,3:4,5:6}, 1, 5, 7)' is '{1:2,5:6}'.

  mapsum
    (class=maps variadic): With 0 args, returns empty map. With >= 1 arg, returns a map with
    key-value pairs from all arguments. Rightmost collisions win, e.g. 'mapsum({1:2,3:4},{1:5})' is '{1:5,3:4}'.

  splitkv
    (class=maps #args=3): Splits string by separators into map with type inference.
    E.g. 'splitkv("a=1,b=2,c=3", "=", ",")' gives '{"a" : 1, "b" : 2, "c" : 3}'.

  splitkvx
    (class=maps #args=3): Splits string by separators into map without type inference (keys and
    values are strings). E.g. 'splitkv("a=1,b=2,c=3", "=", ",")' gives

  splitnv
    (class=maps #args=2): Splits string by separator into integer-indexed map with type inference.
    E.g. 'splitnv("a,b,c" , ",")' gives '{1 : "a", 2 : "b", 3 : "c"}'.

  splitnvx
    (class=maps #args=2): Splits string by separator into integer-indexed map without type
    inference (values are strings). E.g. 'splitnv("4,5,6" , ",")' gives '{1 : "4", 2 : "5", 3 : "6"}'.

KEYWORDS FOR PUT AND FILTER

  all
    all: used in "emit", "emitp", and "unset" as a synonym for @*

  begin
    begin: defines a block of statements to be executed before input records
    are ingested. The body statements must be wrapped in curly braces.
    Example: 'begin { @count = 0 }'

  bool
    bool: declares a boolean local variable in the current curly-braced scope.
    Type-checking happens at assignment: 'bool b = 1' is an error.

  break
    break: causes execution to continue after the body of the current
    for/while/do-while loop.

  call
    call: used for invoking a user-defined subroutine.
    Example: 'subr s(k,v) { print k . " is " . v} call s("a", $a)'

  continue
    continue: causes execution to skip the remaining statements in the body of
    the current for/while/do-while loop. For-loop increments are still applied.

  do
    do: with "while", introduces a do-while loop. The body statements must be wrapped
    in curly braces.

  dump
    dump: prints all currently defined out-of-stream variables immediately
      to stdout as JSON.
      With >, >>, or |, the data do not become part of the output record stream but
      are instead redirected.
      The > and >> are for write and append, as in the shell, but (as with awk) the
      file-overwrite for > is on first write, not per record. The | is for piping to
      a process which will process the data. There will be one open file for each
      distinct file name (for > and >>) or one subordinate process for each distinct
      value of the piped-to command (for |). Output-formatting flags are taken from
      the main command line.
      Example: mlr --from f.dat put -q '@v[NR]=$*; end { dump }'
      Example: mlr --from f.dat put -q '@v[NR]=$*; end { dump >  "mytap.dat"}'
      Example: mlr --from f.dat put -q '@v[NR]=$*; end { dump >> "mytap.dat"}'
      Example: mlr --from f.dat put -q '@v[NR]=$*; end { dump | "jq .[]"}'

  edump
    edump: prints all currently defined out-of-stream variables immediately
      to stderr as JSON.
      Example: mlr --from f.dat put -q '@v[NR]=$*; end { edump }'

  elif
    elif: the way Miller spells "else if". The body statements must be wrapped
    in curly braces.

  else
    else: terminates an if/elif/elif chain. The body statements must be wrapped
    in curly braces.

  emit
    emit: inserts an out-of-stream variable into the output record stream. Hashmap
      indices present in the data but not slotted by emit arguments are not output.
      With >, >>, or |, the data do not become part of the output record stream but
      are instead redirected.
      The > and >> are for write and append, as in the shell, but (as with awk) the
      file-overwrite for > is on first write, not per record. The | is for piping to
      a process which will process the data. There will be one open file for each
      distinct file name (for > and >>) or one subordinate process for each distinct
      value of the piped-to command (for |). Output-formatting flags are taken from
      the main command line.
      You can use any of the output-format command-line flags, e.g. --ocsv, --ofs,
      etc., to control the format of the output if the output is redirected. See also mlr -h.
      Example: mlr --from f.dat put 'emit >  "/tmp/data-".$a, $*'
      Example: mlr --from f.dat put 'emit >  "/tmp/data-".$a, mapexcept($*, "a")'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit @sums'
      Example: mlr --from f.dat put --ojson '@sums[$a][$b]+=$x; emit > "tap-".$a.$b.".dat", @sums'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit @sums, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit @*, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit >  "mytap.dat", @*, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit >> "mytap.dat", @*, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit | "gzip > mytap.dat.gz", @*, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit > stderr, @*, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit | "grep somepattern", @*, "index1", "index2"'
      Please see http://johnkerl.org/miller/doc for more information.

  emitf
    emitf: inserts non-indexed out-of-stream variable(s) side-by-side into the
      output record stream.
      With >, >>, or |, the data do not become part of the output record stream but
      are instead redirected.
      The > and >> are for write and append, as in the shell, but (as with awk) the
      file-overwrite for > is on first write, not per record. The | is for piping to
      a process which will process the data. There will be one open file for each
      distinct file name (for > and >>) or one subordinate process for each distinct
      value of the piped-to command (for |). Output-formatting flags are taken from
      the main command line.
      You can use any of the output-format command-line flags, e.g. --ocsv, --ofs,
      etc., to control the format of the output if the output is redirected. See also mlr -h.
      Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf @a'
      Example: mlr --from f.dat put --oxtab '@a=$i;@b+=$x;@c+=$y; emitf > "tap-".$i.".dat", @a'
      Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf @a, @b, @c'
      Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf > "mytap.dat", @a, @b, @c'
      Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf >> "mytap.dat", @a, @b, @c'
      Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf > stderr, @a, @b, @c'
      Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf | "grep somepattern", @a, @b, @c'
      Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf | "grep somepattern > mytap.dat", @a, @b, @c'
      Please see http://johnkerl.org/miller/doc for more information.

  emitp
    emitp: inserts an out-of-stream variable into the output record stream.
      Hashmap indices present in the data but not slotted by emitp arguments are
      output concatenated with ":".
      With >, >>, or |, the data do not become part of the output record stream but
      are instead redirected.
      The > and >> are for write and append, as in the shell, but (as with awk) the
      file-overwrite for > is on first write, not per record. The | is for piping to
      a process which will process the data. There will be one open file for each
      distinct file name (for > and >>) or one subordinate process for each distinct
      value of the piped-to command (for |). Output-formatting flags are taken from
      the main command line.
      You can use any of the output-format command-line flags, e.g. --ocsv, --ofs,
      etc., to control the format of the output if the output is redirected. See also mlr -h.
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp @sums'
      Example: mlr --from f.dat put --opprint '@sums[$a][$b]+=$x; emitp > "tap-".$a.$b.".dat", @sums'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp @sums, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp @*, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp >  "mytap.dat", @*, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp >> "mytap.dat", @*, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp | "gzip > mytap.dat.gz", @*, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp > stderr, @*, "index1", "index2"'
      Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp | "grep somepattern", @*, "index1", "index2"'
      Please see http://johnkerl.org/miller/doc for more information.

  end
    end: defines a block of statements to be executed after input records
    are ingested. The body statements must be wrapped in curly braces.
    Example: 'end { emit @count }'
    Example: 'end { eprint "Final count is " . @count }'

  eprint
    eprint: prints expression immediately to stderr.
      Example: mlr --from f.dat put -q 'eprint "The sum of x and y is ".($x+$y)'
      Example: mlr --from f.dat put -q 'for (k, v in $*) { eprint k . " => " . v }'
      Example: mlr --from f.dat put  '(NR % 1000 == 0) { eprint "Checkpoint ".NR}'

  eprintn
    eprintn: prints expression immediately to stderr, without trailing newline.
      Example: mlr --from f.dat put -q 'eprintn "The sum of x and y is ".($x+$y); eprint ""'

  false
    false: the boolean literal value.

  filter
    filter: includes/excludes the record in the output record stream.
      Example: mlr --from f.dat put 'filter (NR == 2 || $x > 5.4)'
      Instead of put with 'filter false' you can simply use put -q.  The following
      uses the input record to accumulate data but only prints the running sum
      without printing the input record:
      Example: mlr --from f.dat put -q '@running_sum += $x * $y; emit @running_sum'

  float
    float: declares a floating-point local variable in the current curly-braced scope.
    Type-checking happens at assignment: 'float x = 0' is an error.

  for
    for: defines a for-loop using one of three styles. The body statements must
    be wrapped in curly braces.
    For-loop over stream record:
      Example:  'for (k, v in $*) { ... }'
    For-loop over out-of-stream variables:
      Example: 'for (k, v in @counts) { ... }'
      Example: 'for ((k1, k2), v in @counts) { ... }'
      Example: 'for ((k1, k2, k3), v in @*) { ... }'
    C-style for-loop:
      Example:  'for (var i = 0, var b = 1; i < 10; i += 1, b *= 2) { ... }'

  func
    func: used for defining a user-defined function.
    Example: 'func f(a,b) { return sqrt(a**2+b**2)} $d = f($x, $y)'

  if
    if: starts an if/elif/elif chain. The body statements must be wrapped
    in curly braces.

  in
    in: used in for-loops over stream records or out-of-stream variables.

  int
    int: declares an integer local variable in the current curly-braced scope.
    Type-checking happens at assignment: 'int x = 0.0' is an error.

  map
    map: declares an map-valued local variable in the current curly-braced scope.
    Type-checking happens at assignment: 'map b = 0' is an error. map b = {} is
    always OK. map b = a is OK or not depending on whether a is a map.

  num
    num: declares an int/float local variable in the current curly-braced scope.
    Type-checking happens at assignment: 'num b = true' is an error.

  print
    print: prints expression immediately to stdout.
      Example: mlr --from f.dat put -q 'print "The sum of x and y is ".($x+$y)'
      Example: mlr --from f.dat put -q 'for (k, v in $*) { print k . " => " . v }'
      Example: mlr --from f.dat put  '(NR % 1000 == 0) { print > stderr, "Checkpoint ".NR}'

  printn
    printn: prints expression immediately to stdout, without trailing newline.
      Example: mlr --from f.dat put -q 'printn "."; end { print "" }'

  return
    return: specifies the return value from a user-defined function.
    Omitted return statements (including via if-branches) result in an absent-null
    return value, which in turns results in a skipped assignment to an LHS.

  stderr
    stderr: Used for tee, emit, emitf, emitp, print, and dump in place of filename
      to print to standard error.

  stdout
    stdout: Used for tee, emit, emitf, emitp, print, and dump in place of filename
      to print to standard output.

  str
    str: declares a string local variable in the current curly-braced scope.
    Type-checking happens at assignment.

  subr
    subr: used for defining a subroutine.
    Example: 'subr s(k,v) { print k . " is " . v} call s("a", $a)'

  tee
    tee: prints the current record to specified file.
      This is an immediate print to the specified file (except for pprint format
      which of course waits until the end of the input stream to format all output).
      The > and >> are for write and append, as in the shell, but (as with awk) the
      file-overwrite for > is on first write, not per record. The | is for piping to
      a process which will process the data. There will be one open file for each
      distinct file name (for > and >>) or one subordinate process for each distinct
      value of the piped-to command (for |). Output-formatting flags are taken from
      the main command line.
      You can use any of the output-format command-line flags, e.g. --ocsv, --ofs,
      etc., to control the format of the output. See also mlr -h.
      emit with redirect and tee with redirect are identical, except tee can only
      output $*.
      Example: mlr --from f.dat put 'tee >  "/tmp/data-".$a, $*'
      Example: mlr --from f.dat put 'tee >> "/tmp/data-".$a.$b, $*'
      Example: mlr --from f.dat put 'tee >  stderr, $*'
      Example: mlr --from f.dat put -q 'tee | "tr [a-z\] [A-Z\]", $*'
      Example: mlr --from f.dat put -q 'tee | "tr [a-z\] [A-Z\] > /tmp/data-".$a, $*'
      Example: mlr --from f.dat put -q 'tee | "gzip > /tmp/data-".$a.".gz", $*'
      Example: mlr --from f.dat put -q --ojson 'tee | "gzip > /tmp/data-".$a.".gz", $*'

  true
    true: the boolean literal value.

  unset
    unset: clears field(s) from the current record, or an out-of-stream or local variable.
      Example: mlr --from f.dat put 'unset $x'
      Example: mlr --from f.dat put 'unset $*'
      Example: mlr --from f.dat put 'for (k, v in $*) { if (k =~ "a.*") { unset $[k] } }'
      Example: mlr --from f.dat put '...; unset @sums'
      Example: mlr --from f.dat put '...; unset @sums["green"]'
      Example: mlr --from f.dat put '...; unset @*'

  var
    var: declares an untyped local variable in the current curly-braced scope.
    Examples: 'var a=1', 'var xyz=""'

  while
    while: introduces a while loop, or with "do", introduces a do-while loop.
    The body statements must be wrapped in curly braces.

  ENV
    ENV: access to environment variables by name, e.g. '$home = ENV["HOME"]'

  FILENAME
    FILENAME: evaluates to the name of the current file being processed.

  FILENUM
    FILENUM: evaluates to the number of the current file being processed,
    starting with 1.

  FNR
    FNR: evaluates to the number of the current record within the current file
    being processed, starting with 1. Resets at the start of each file.

  IFS
    IFS: evaluates to the input field separator from the command line.

  IPS
    IPS: evaluates to the input pair separator from the command line.

  IRS
    IRS: evaluates to the input record separator from the command line,
    or to LF or CRLF from the input data if in autodetect mode (which is
    the default).

  M_E
    M_E: the mathematical constant e.

  M_PI
    M_PI: the mathematical constant pi.

  NF
    NF: evaluates to the number of fields in the current record.

  NR
    NR: evaluates to the number of the current record over all files
    being processed, starting with 1. Does not reset at the start of each file.

  OFS
    OFS: evaluates to the output field separator from the command line.

  OPS
    OPS: evaluates to the output pair separator from the command line.

  ORS
    ORS: evaluates to the output record separator from the command line,
    or to LF or CRLF from the input data if in autodetect mode (which is
    the default).

AUTHOR

Miller is written by John Kerl <kerl.john.r@gmail.com>.

This manual page has been composed from Miller's help output by Eric MSP Veith <eveith@veith-m.de>.

SEE ALSO

awk(1), sed(1), cut(1), join(1), sort(1), RFC 4180: Common Format and MIME Type for Comma-Separated Values (CSV) Files, the miller website http://johnkerl.org/miller/doc