Awk

expand some_file | awk '{if (x < length()) x = length() } END { print “Longest row is ” x }'

awk 'NF > 0' some_file

Count lines

awk 'END {print NR}' some_file

Awk as Grep

awk '{print $2}' some_file

which is a quicker alternative to cat some_file | awk '{print $2}'

To negate a pattern (print only lines that don’t match), use awk '$1 !~ /regexp/' some_file

Strings substitution

awk '{sub("from", "to"); print}'

substitutes “from” to “to”. With {gsub("from", "to"); print} it substitutes all occurrences and not just the first. Both can be used with regexps, like /regexp/', 'new_string'

Comparison

awk '$2 > 1'

print only lines where $2 is bigger than 1

awk '$1 > 1 && < 10'

multiple comparisons (bigger than 1 and smaller than 10)

==

equality

~

matching (even a regexp)

awk '!a[$0]++' file

Regexp matching

awk '$0 ~ "[A-Za-z0-9]+" {print $1}'

print $1 only if $0 matches the regexp

Variables in Awk

awk -v var="bang" '{sub(var,"boom");print}'

it also accepts shell variables with -v var=$shell_variable

Environment variables can also be accessed with awk '{print, $0,ENVIRON["x"]}' some_file

Dates in Awk

awk '{print strftime("%d-%m-%y %H-%M-%S", systime());}'

strftime converts the output of systime from the Unix epoch to a more human-readable format. Pattern is the same as date command. systime can be omitted (it defaults to current time). Only in GNU awk.

awk '{$1=$2=""; print $0}'