README.md

Useful Perl Oneliners

Very usefull Perl one liners, designed to be used inside shell scripts.

First occurrence of regular expression

Command   :   perl -ne 'print "$1" and exit if /(REGEX_HERE)/'

Last occurrence of regular expression

Command   :   perl -ne '$e = $1 if /(REGEX_HERE)/;  END{ print $e }'

Print something if regex matches

Command   :   perl -ne 'print /(REGEX_HERE)/ ? "match" : "no-match" '
Example   :   echo "ABC123" | perl -ne 'print /ABC123/ ? "match" : "no-match" '  
Output    :   match

Print content of specific column (separated by spaces)

Command   :   perl -lane 'print $F[0]'
Example   :   echo "A B C" | perl -lane 'print $F[0]'
Output    :   A

Print content of specific column (separated by any character)

Command   :   perl -F[CHARACTER_HERE] -a -ne 'print "$F[0]" '
Example   :   echo "A;B;C" | perl -F; -a -ne 'print "$F[1]" '
Output    :   B

Print something if columns match specific regex

Command   :   perl -lane 'print "TRUE" if $F[0]=~/\d/ and $F[1]=~/\D/'
Example   :   echo "3 z" | perl -lane 'print "TRUE" if $F[0]=~/\d/ and $F[1]=~/\D/'
Output    :   TRUE

Sobstitute match in file

-pi.orig will create a backup of the file with ".orig" at the end

Command   :   perl -pi.orig -e 's/(REGEX_HERE)/(VALUE_HERE)/' (PATH_TO_FILE)

Check syntax of file (parse)

eg. in this case file format must be KEY;VALUE

Command   :   perl -ne '$exit_code='0' ; $exit_code='1' if $_ !~ /.*?\s;\s.*/ ; print "1" and exit if $exit_code' (PATH_TO_FILE)

Substitute multiple placeholders with one single one liner

File: example_config_file.txt (with placeholders)

<VirtualHost *:80>
    DocumentRoot ##DOCUMENT_ROOT##
    ServerName ##SERVER_NAME##
</VirtualHost>

File: script.sh

export DOCUMENT_ROOT="/var/www/"
export SERVER_NAME="example.com"
perl -pi.orig -w -e 's!##(.+?)##!$ENV{$1}!ge;' example_config_file.txt

Get the current time five minutes ago

POSIX format

perl -MPOSIX=strftime -le 'print strftime("%Y-%m-%d %H:%M:%S", localtime(time()-5*60))'

EPOC format

date -d "$(perl -MPOSIX=strftime -le 'print strftime("%Y-%m-%d %H:%M:%S", localtime(time()-5*60))')" +%s