cols.md

Motivation

This is a faster to key stroke (& execute) version of awk '{print $X}'. It also acts as demo/example code for some library APIs from cligen/ & was a very early member of cligen/examples/ itself.

Something it provides over the awk invocation is

• the ability to delete indicated columns (with -c, --cut).

Things it provides over both awk & GNU coreutils cut are the ability to:

• shift column-numbering origins (e.g. 0 | 1-origin)
• do either inclusive (..) OR exclusive (:) ranges/slices
• allows numbers < 0 to mean from-the-end (like Python) { use -- or \-escape (or quote) whitespace before '-' to avoid treatment as an option }.

Over just cut it provides:

• default to keep; more terse CL syntax than "--complement"
• ability to split 1 column on repeated bytes (like awk)

Usage

  cols [optional-params] colNums or A..B | X:Y (in|ex)clusive ranges thereof

Write just some columns of input to output; Memory map input if possible.

  -i=, --input=  string "/dev/stdin"  path to mmap|read as input
  -r=, --rowDlm= char   '\n'          inp row delimiter character
  -d=, --delim=  string "white"       inp field dlm chars; len>0 => fold
  -o=, --output= string "/dev/stdout" path to write output file
  -s=, --sepOut= string " "           output field separator
  -b, --blanksOk bool   false         allow blank output rows
  -c, --cut      bool   false         cut/censor specified columns, not keep
  --origin=      int    1             origin for colNums; 0=>signed indexing
  -0, --O0       bool   false         shorthand for --origin=0
  -t=, --term=   char   '\n'          set output row terminator (e.g. \0)

Examples

After:

(echo 1 2 3 4; echo; echo 4 5 6 7) > /tmp/d

you get:

cols 2 4 < /tmp/d

producing

2 4
5 7

With cols -c0 -- -4..-3 you get:

3 4
6 7

since you are cutting 0-origin 4th from end & 3rd from end. Meanwhile with cols -0 1:3 you get:

2 3
5 6

since you are keeping the exclusive slice indicating 0-origin 1 & 2.

With all of them if you add -b the blank row propagates, or you can make the output separated TAB or terminator NUL, etc.

That's it, really. This intends to be a very simple utility. Among the most advanced examples I can think of is :

ls -l --zero | cols -cr\\0 1..4 -t\\0

to produce a list of 0-terminated rows where (for GNU ls) the first 4 columns are guaranteed to be space separated and any newlines are from path names. The consumer of that output data needs to remain careful, of course.