Why is the list my Perl map returns just 1's?

Question

The code I wrote is as below :

#!/usr/bin/perl 

my @input = ( \"a.txt\" , \"b.txt\" , \"c.txt\" ) ;
my @output = map { $_ =~ s/\\..*$// } @input ;

print @o         


        

Answer 1

You are missing the 's' for substitution.

$_ =~ /\..*$//

should be

$_ =~ s/\..*$//

Also you might be better off to use s/\.[^\.]*$// as your regular expression to make sure you just remove the extension even when the filename contains a '.' (dot) character.

Answer 2

Ok, first off, you probably meant to have $_ =~ s/\..*$// — note the missing s in your example. Also, you probably mean map not grep.

Second, that doesn't do what you want. That actually modifies @input! Inside grep (and map, and several other places), $_ is actually aliased to each value. So you're actually changing the value.

Also note that pattern match does not return the matched value; it returns true (if there is a match) or false (if there isn't). That's all the 1's you're seeing.

Instead, do something like this:

my @output = map {
    (my $foo = $_) =~ s/\..*$//;
    $foo;
} @input ;

The first copies $_ to $foo, and then modifies $foo. Then, it returns the modified value (stored in $foo). You can't use return $foo, because its a block, not a subroutine.