field [options] [args]
  select and output fields from each record of stdin

args:
  - 1-arg: field [options] <rangelist>
  - 2-arg: field [non-field opts] <indelim> <rangelist>
  - 3-arg: field [non-field opts] <indelim> <outdelim> <rangelist>
  - if -r/--regex, indelim is a python regular expression
  - field and record delimiters can also be given as options
  - fixed delimiters are python string literals
  - regex delimiters are python raw strings

fields:
  - defaults to whitespace: 'bytes.split(sep=None)'
  - if supplied as $1, uses 'bytes.split(sep="$1")'
  - if '-r', uses 're.split(r'$1')'
  - if '-i <value>', uses 'bytes.split(sep="<value>")'
  - if '-F <value>', uses 're.split(r"<value>")'
  - if $IFS set, splits on its chars: 're.split(f"[{getenv(IFS)}]+")'
  - if '-e', all empty fields are discarded
  - if '-G', only leading or trailing blank fields are discarded

records:
  - defaults to newline: 'bytes.split(sep="\n")'
  - if '-I <value>', uses 'bytes.split(sep="<value>")'
  - if '-R <value>', uses 're.split(r"<value>")'
  - if '-E', empty records in input are discarded
  - if '-N', trailing separator on last record not emitted
  - processes input as bytes, in chunks of io.DEFAULT_BUFFER_SIZE
  - chunk size overridden with '-b/--bsz' (optional k or m suffix)

outdelims:
  - fields default to space, ie '\x20', or via $2, or via -o/--ofs
  - records default to newline, ie '\n', or via -O/--ors

rangelist:
  - specifier is a comma separated list of ranges
  - ranges are either single numbers or first-last sequences
  - unspecified Y in X-Y will default to highest Y in the input
  - if first field in range greater than than last, print reversed
  - if any specified fields do not exist in the record, skip them
  - field '0' is the same as all fields (range '1-')

range:
      N: just field number N (1 is first)
     -N: just field Nth from the end (-1 is last)
    N-M: fields N through M (M > N)
    N-M: fields M through N, backwards (N > M)
     N-: fields N through the end
    -N-: fields from Nth from the end, through the end
   N--M: fields N through Mth from end
  -N--M: fields Nth from the end through Mth from the end

examples:
  "echo one two three four five | field 2 -> "two"
  "echo one two three four five | field -2" -> "four"
  "echo one two three four five | field 2-4" -> "two three four"
  "echo one two three four five | field 4-2" -> "four three two"
  "echo one two three four five | field 3-" -> "three four five"
  "echo one two three four five | field -2-" -> "four five"
  "echo one two three | field 1,0" -> "one one two three"
  "echo {1..12} | field -8--10" -> "5 4 3"
  "echo {1..12} | field -8--15" -> "5 4 3 2 1"
  "echo {1..12} | field 3--15" -> "3 2 1"
  "echo {1..12} | field 1-3,-1--2,8,8,10-,-2" -> "1 2 3 12 11 8 8 10 11 12 11"

todo:
  - read from files given as additional arguments
  - /R/-/S/: starting with /R/ and ending with /S/
  - specify record selection criteria (pattern)
  - field reformatting, eg wrapping, fit in column or on page
  - args like -g columnate_group
  - different behaviors for range overlaps (set union, addition)
  - way to disinclude fields ("all fields except...")
  - multiple delimiters, maybe a -i and -d possible for every -f
  - multiple delimiters, as in multiple patterns will serve as one
  - implement a "record" in terms of "field?"
  - flag to discard empty records in output (no non-empty fields)