Perl，将正则表达式匹配赋予标量

Question

There's an example snippet in Mail::POP3Client in which theres a piece of syntax that I don't understand why or how it's working:

foreach ( $pop->Head( $i ) ) {
    /^(From|Subject):\s+/i and print $_, "\n";
}

The regex bit in particular. $_ remains the same after that line but only the match is printed. An additional question; How could I assign the match of that regex to a scalar of my own so I can use that instead of just print it?

Answer 1

This is actually pretty tricky. What it's doing is making use of perl's short circuiting feature to make a conditional statement. it is the same as saying this.

if (/^(From|Subject):\s+/i) { 
    print $_;
}

It works because perl stops evaluating and statements after something evaluates to 0. and unless otherwise specified a regex in the form /regex/ instead of $somevar =~ /regex/ will apply the regex to the default variable, $_

you can store it like this

my $var;    
if (/^(From|Subject):\s+/i) { 
        $var = $_;
}

or you could use a capture group

/^((?:From|Subject):\s+)/i

which will store the whole thing into $1