Re: How to conditionally substitute in files?

Siegfried Heintze (Aditi) wrote:
> This works:
> 
> perl -i.bak -ple "s/class/xybpublicabc/g" Migration.cs
> 
> However, when there are no matches, it still creates a new .bak file.
> 
> How can we not change the date time on a file if there are no substitutions make?

You have to code it that way explicitly yourself, something like (UNTESTED):


my $file = 'Migration.cs';

open my $IN,  '<', $file       or die "Cannot open '$file' $!";
open my $OUT, '>', "$file.new" or die "Cannot open '$file.new' $!";

my $changed;
while ( <$IN> ) {
     $changed += s/class/xybpublicabc/g;
     print $OUT;
     }

close $OUT;
close $IN;

if ( $changed ) {
     rename $file, "$file.bak" or die "Cannot rename '$file' $!";
     rename "$file.new", $file or die "Cannot rename '$file.new' $!";
else {
     unlink "$file.new" or die "Cannot unlink '$file.new' $!";
     }

__END__



John
-- 
Perl isn't a toolbox, but a small machine shop where you
can special-order certain sorts of tools at low cost and
in short order.                            -- Larry Wall