GNU awk

gawk - pattern scanning and processing language

AWK is named after the surnames of its three authors, who are Alfred Aho, Peter Weinberger, and Brian Kernighan.

mawk, gawk

Pre-defined variables in awk

• $0: entire current record/line
• $1, $2, ...: the first, second,... fields in current record/line
• NF: number of fields
• NR: number of records/lines

Built-in functions

Examples

Print the first column of /etc/passwd file. The /etc/passwd uses ':' (colon) as separator between columns.

$ awk -F: '{ print $1}' /etc/passwd

Print process id (PID) column

ps | print '{print $1}'

Create get_tags_pre.awk file with content

/<pre>/,/<\/pre>/ { print; }

Get all content inside <pre> tags

cat inputfile.txt | awk -f get_tags_pre.awk > outputfile.txt

Get just indented lines below "Standard IP access list 11"

root@T420:~# cat acl1.txt |  awk '/access list 11/ && !f{f=1;x=$0;sub(/[^ ].*/,"",x);x=x" ";print;next} f {if (substr($0,1,length(x))==x)print; else f=0}'
Standard IP access list 11
    10 permit 212.1.116.12

Print parent rule and subrules in checkpoint firewall

awk -F";" -v parentrule="" 'BEGIN{print "===START==="}; $2 ~ /8030 -/ || $1 ~ parentrule {split($1,array,".");parentrule=array[1]; print $0;}; END{print "\n===END===\n";}' samplerule.csv

References

The GNU Awk User’s Guide

Books about gawk

GAWK: Effective AWK Programming by Arnold D. Robbins

Courses about awk

Linux Administration with sed and awk | Andrew Mallett

Practice

>>> THM | Linux Modules