First, $_ eq 'abc' is faster than /^abc$/.

If you want 0 or 1:

my $f = !!grep { $_ eq 'abc' } @a;
if ($f) { ... }
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True or false will probably suffice:

my $f = grep { $_ eq 'abc' } @a;
if ($f) { ... }
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You can get rid of the flag entirely:

if (grep { $_ eq 'abc' } @a) { ... }
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More important than that it’s faster is that it expresses what happens more directly. With the pattern match, you have to mentally parse the pattern to figure out what is going on. $_ eq 'abc' is much quicker to read.

Makeshifts last the longest.

nice examples!, but what does !! do ?

Luca

It's two negation operators. In scalar context ("!" imposes a scalar context), grep returns the number of matching elements. Negating this twice converts zero to false, and non-zero to true. False is 0 when used as a number. True is 1 when used as a number.

For example,

                   | Ex. 1 | Ex. 2
-------------------+-------+------
grep returns       | 4     | 0
1st negation op    | false | true
2nd negation op    | true  | false
When used as a num | 1     | 0
When used as a str | '1'   | ''
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  #!/usr/bin/perl -w
use strict;
my @a;
my $f;
$a[0] = "a" ;
$a[1] = "c" ;
$a[2] = "abcd" ;
$a[3] = "b" ;

($f) = grep {$a[$_] =~ /^abc$/} (0..$#a);# ? 1 : 0;
if ( $f ) {
    print "YES\n" ;
}
1;
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#!/usr/bin/perl -w
use strict;
my (@f) = qw|a ab abc abcd|;

if (grep {/Zabc/} @f){
    print 'YES!';
}
1;
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 In scalar context, returns the number of times the
 expression was true.
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