[SOLVED] search 2 strings and prepend string3 at the beginning of matched line

Issue

I want to search 1st string 'abc' in each line of a file and if exists, search for 2nd string 'xyz' on the same matched line, then prepend 3rd string '//' at the beginning of matched line.

I tried below command, but it only prints output but does not make changes to existing file. Please help here.

grep 'abc' myfile | grep 'xyz' | sed 's/^/\/\//'

Solution

Use this Perl one-liner:

perl -i.bak -lpe 'm{abc} and m{xyz} and $_ = "//$_"; ' in_file

The Perl one-liner uses these command line flags:
-e : Tells Perl to look for code in-line, instead of in a file.
-p : Loop over the input one line at a time, assigning it to $_ by default. Add print $_ after each loop iteration.
-l : Strip the input line separator ("\n" on *NIX by default) before executing the code in-line, and append it when printing.
-i.bak : Edit input files in-place (overwrite the input file). Before overwriting, save a backup copy of the original file by appending to its name the extension .bak. If you want to skip writing a backup file, just use -i and skip the extension.

See also:

• perldoc perlrun: how to execute the Perl interpreter: command line switches
• perldoc perlrequick: Perl regular expressions quick start
• perldoc perlvar: Perl predefined variables

Answered By - Timur Shtatland

Answer Checked By - David Marino (WPSolving Volunteer)