mainly for text processing, reformatting & transformations

• extract the first column from a file: awk '{print $1}' file

• renaming files (append ‘.new’): ls files_list | awk '{print "mv "$1" "$1".new"}' | sh

• renaming within a name: ls -1 *old* | awk '{print "mv "$1" "$1}' | sed s/old/new/2 | sh

• remove only files:

  • ls -l * | grep -v drwx | awk '{print "rm "$9}' | sh
  • ls -l|awk '$1!~/^drwx/{print $9}'|xargs rm

• remove only directories:

  • ls -l | grep '^d' | awk '{print "rm -r "$9}' | sh
  • ls -p | grep /$ | wk '{print "rm -r "$1}'
  • ls -l|awk '$1~/^d.*x/{print $9}'|xargs rm -r

• killing processes by name, eg. netscape:

  • kill ps auxww | grep netscape | egrep -v grep | awk '{print $2}'
  • ps auxww | awk '$0~/netscape/&&$0!~/awk/{print $2}' |xargs kill

• rearranging columns:

  • 1234 HD 13324 22:40:54
  • 1235 HD122235 22:43:12
  • awk ‘{ printf $NF;$NF = “” ;printf ” “$0”\n” }’ | sort
  • 22:40:54 1234 HD 13324
  • 22:43:12 1235 HD122235

• pretty printing tables (with header & footer)

  awk 'BEGIN {  print "Month Crates"
                print "----- ------" }
             {  print $1, "   ", $2  }
       END   {  print "----- ------" }' testfile

• where testfile contains:

Jan 13
Feb 15
Mar 15

• working over a subset of lines instead of all lines in file

  • precede by <condition>
  • examples:
  • print entire line of all lines in hosts file starting with “127.0.0.1”: awk '/^127.0.0.1 missscatterbrain/ {print}' /etc/hosts
  • print line where 7th item contains “bash”: awk -F: '$7 ~ /bash/ {print $1}' /etc/passwd | sort

• as a programming language

  • implements necessary flow control structures
  • a set of operators
  • predefined functions to deal with numbers & strings
  • user defined functions
  • able to manage common scalar vars & variable sized arrays
  • libraries exist: gawk