====== AWK cheatsheet ======


Ever since I started using ''awk'' in [[http://p.outlyer.net/vcs/|vcs]] I've been finding about its power but I'm unable to remember its syntax so here's a series of notes.

General notes:
  * Use ''mawk'' instead of ''gawk'' when trying syntax for better cross-compatibility. Debian also has ''original-awk''.
  * Non-GNU awk doesn't understand Perl Regexes
  * ''-F'' defines the field separator
  * Profiling can be done with ''pgawk'' which produces an ''awkprof.out'' file with execution numbers for each statement

Books:
  * [[http://www.gnu.org/software/gawk/manual/|Gawk: Effective AWK Programming]] (FSF)
  * [[http://my.safaribooksonline.com/1-56592-225-5|sed & awk, 2nd Edition]] (O'Reilly)

===== Command-equivalents =====

  * ''**cut**'': ''cut -d: -f2'' => ''awk -F: '{ print $2 }' ''
  * ''**grep**'': ''grep REGEX'' => ''awk /REGEX/''
    * (GNU -also in FreeBSD-) grep appears to understand Perl character classes (i.e. ''\w'') 
  * ''**grep -v**'': ''grep -v REGEX'' => ''awk '! /REGEX/' ''
    * Equivalent sed: ''sed /REGEX/ d''

===== Text replacements =====

''sub()'' and ''gsub()''. Either strings or regexs can be used

  $ echo hello world | awk 'sub("hello", "bye")'
  > bye world

  * Prepend to each line: ''sed 's/^/PREP: /' '' => ''awk 'sub("", "PREP: ")' '' or ''awk 'sub(/^/, "PREP: ")' '' <code>
  $ echo -e 'hello\nbye' | awk 'sub(/^/, "PREP: ")'
  > PREP: hello
  > PREP: bye</code>
  * Append to each line: ''sed 's/$/: APP/' '' => ''awk 'sub(/$/, ": APP")' ''<code>
  $ echo -e 'hello\nbye' | awk 'sub(/$/, ": APP")'
  > hello: APP
  > bye: APP</code>