#!/usr/bin/perl
use strict;
use warnings;
use File::Slurper qw(read_text write_text);

my $filename = 'in.txt';

my $data = read_text($filename);
$data =~ s/The action failed\./failed_build/g;
write_text($filename, $data);

__END__

$ cat in.txt
one
two
The action failed.
three
The action failed.  twice The action failed.
four

$ cat in.txt
one
two
failed_build
three
failed_build  twice failed_build
four