AWK is an interpreted programming language. It’s designed for text processing. Input is read line by line and awk script/command is executed.

Basic examples

• Input processing

  • Get input from input.txt file and process file line by line: awk '{ }' input.txt
  • Get piped input and process output line by line: cat input.txt | awk '{}'

• Read input.txt and print the 3rd word from each line: awk '{ print $3 }' input.txt

• Read input line by line, and print each line: cat input.txt | awk '{print $0}'

• Check for pattern, if found print first word: awk ' /pattern/ {print $1}' input.txt

• If str matches with 2nd word, print 3rd word: awk '$2=="str" {print $3}' input.txt

• Specify field saperator for parsed line: awk -F'&' '$2=="str" {print $3}' input.txt
  • Now each field i.e. $1, $2 will be string saperated by ‘&’ unlike ‘space’ is default case.

• If 1st word partly matches str, then print 3rd word: awk '$1 ~ "str" {print $3}' input.txt

• Ignorecase string comparision, if 2nd element is “find/Find/fInd/fiND”, then print third element :

  awk '{ if (tolower($2) == "find") print $3}' input.txt

BEGIN, END and NR are some of in-built variables in AWK

• Variable in awk:
  • BEGIN block runs only once and at beginning.

    awk -v name=Jerry 'BEGIN{printf "Name = %s\n", name}'

• Add two numbers:

  awk ' BEGIN { a = 50; b = 20; print "(a + b) = ", (a + b) }'

• Read number of lines in file.
  • END block executes after executing all the awk codes.
  • NR is in-built variable which line number is excuted.

    awk 'END { print NR }' inputfile

• Using BEGIN, END and NR

  awk 'BEGIN{print "Begin";print "multiple"} {print "Line " NR ":" $0 }END{print "END"} inputfile

• Looping and other construct are also there, which you can read from here, but above basic stuff will get you started.

References: Tutorials Point: http://www.tutorialspoint.com/awk/