Introduction to AWK


The basic function of awk is to search files for lines or other text units containing one or more patterns. When a line matches one of the patterns, special actions are performed on that line.

Display user names from /etc/passwd (field 1): 
awk -F: '{ print $1 }' /etc/passwd
Where F is the field separator; in passwd file, fields are separated by ':' Default field separator is a blank space. Awk scans the input file and splits each input line into fields. Similarly: 
cat /etc/passwd | awk -F: '{ print $1 }'

Display user names home directories and login shell (fields 1 and 7): and store them in a separate file, users.txt 
awk -F: '{ print $1, $6, $7 }' /etc/passwd > users.txt
or 
cat /etc/passwd | awk -F: '{ print $1, $6, $7 }' > users.txt

Default field separator is empty space. To print users (field 1) from just created file users.txt: 
awk '{ print $1 }' users.txt

Recommended tutorial: The GNU awk programming language