Perl Oneliners

One-liners

One-liner: print

-e|command line
-E

perl -e "print 42"

perl -E "say 42"

perl -E "say q(hello world)"

One-liner: Rename many files

rename
glob
Rename every .log file adding an extra extension of .old

perl -e "rename $_, $_ . '.old' for glob '*.log'"

Rename every .log file replacing .log with a timestamp

perl -e "$t = time; rename $_, substr($_, 0, -3) . $t for glob '*.log'"

One-liner: grep on Windows as well

Lacking grep on Windows, search for all the occurrences of the 'secret' in my xml files.

In a single file:

perl -ne "print $_ if /secret/" main.xml

As Windows does not know how to handle wildcards on the command line, we cannot supply *.xml and expect it to handle all the xml files. We help it with a small BEGIN block. $ARGV holds the name of the current file

perl -ne "BEGIN{ @ARGV = glob '*.xml'} print qq{$ARGV:$_} if /secret/"

One-liner: Replace a string in many files

-i
-p

You have a bunch of text files in your directory mentioning the name:

"Microsoft Word"

You are told to replace that by

"OpenOffice Write"

perl -i -p -e "s/Microsoft Word/OpenOffice Write/g" *.txt

-i = inplace editing
-p = loop over lines and print each line (after processing)
-e = command line script

One-liner: Change encoding

-i
-M
-p
Encode

Convert all the .srt files that are Windows Hebrew encoded to UTF-8 keeping a backup copy of the original file with a .bak extension.

-i    - inplace editing
.bak  - generate backup with that extension
-M    - load  module as 'use' would do
-p    - go over line by line on the file, put the line in $_, execute the
        command on it and then print the result.
        In case of inplace editing, save it back to the file.

perl -i.bak -MEncode -p -e "Encode::from_to($_, 'Windows-1255', 'utf-8')" video.srt

use Encode;

foreach $file (@ARGV) {
    copy $file, "$file.bak";
}
while (<>) {
   Encode::from_to($_, 'Windows-1255', 'utf-8');
   print $_;
}

One-liner: print the 3rd field of every line in a CSV file

CSV
-n
-a
-F

You have a number of csv files, you want to print the 3rd field of each row of each file.

perl -n -a -F, -e 'print "$F[2]\n"' *.csv

-n  = loop over lines but do NOT print them
-a  = autosplit by ' '
-F, = replace the split string by ','

You want to make sure all the rows are 4 elements long. Print out file name and line number of all the bad rows.

perl -a -F, -n -e 'print "$ARGV:$.\n" if @F != 4' data.csv

One-liner: Print all usernames from /etc/passwd

perl -n -a -F: -e 'print "$F[0]\n"' /etc/passwd

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Perl Oneliners