How do I perform general pattern assignments in Perl?

Question

$ cat names
projectname_flag_jantemp
projectname_flag_febtemp
projectname_flag_marchtemp
projectname_flag_mondaytemp
$

Perl code:

my $infile = "names";
open my $fpi, '<', $infile or die "$!";
while (<$fpi>) {
    my $temp = # what should come here? #
    func($temp);
}

I want temp to have

jan
feb
march
monday

respectively.

The pattern always remains the same

projectname_flag_<>temp

How should I do the extraction?

Answer 1

while (<$fpi>) {
        chomp;
        s{projectname_flag_(.*?)temp}{$1};
        # $_ will now have jan, feb, ...
}

Answer 2

I guess:

/^projectname_flag_([a-z]+)temp$/

Answer 3

my ($temp) = /^projectname_flag_(.+)temp$/;

Note that the parentheses around $temp are needed so that the pattern match runs in list context. Without them, $temp would end up containing just a true or false value indicating whether the match succeeded.

More generally, a pattern match in list context returns the captured subpatterns (or an empty list if the match fails). For example:

my $str = 'foo 123   456 bar';
my ($i, $j) = $str =~ /(\d+) +(\d+)/;  # $i==123  $j==456

Answer 4

Hi, you could try this.

while (<$fpi>) {
  my ($temp) =($_ =~ m/projectname_flag_(.*?)temp/);
  func($temp);
}

Answer 5

If compatibility with older perls is needed, I would use FM's answer (just make sure the match succeeded by checking if $month is defined).

As of 5.10, you can use named captures:

my $month;
if ( /^ projectname _flag_ (?<month> [a-z]+ ) temp \z/x ) {
    $month = $+{month};
}