use strict;
my $str = '1
00:07:14,120 --> 00:07:16,953
[French line]
[Russian line]
2
00:07:16,960 --> 00:07:19,952
[French line]
[Russian line]
3
00:07:21,240 --> 00:07:24,835
[French line]
[Russian line]';
my $regex = qr/(?:(?:\R|\A).+){3}\K\R.+/mp;
my $subst = '';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html