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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




Extract 14-character-lines from a text file


┌──(root㉿LenovoX230)-[/usr/share/seclists/Usernames]
└─# gawk "length == 14" xato-net-10-million-usernames.txt >> 14-characters.txt




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














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