How can I process a multi line string one line at a time in perl with use strict in place?

Question

I\'m trying to figure out the proper PBP approved way to process a multi line string one line at a time. Many Perl coders suggest treating the multi line string as a filehandle

Answer 1

Open a filehandle using a pipe from "dir" command.

E.g.

open my $FOO, "dir|" or die "Can not run 'dir': $!";

Answer 2

Don't initialise $ResultsHandle:

use strict;
use warnings; 

my $return = `dir`;
my $ResultsHandle;  # <-- leave undefined
my $matchLines = "";
my $resultLine = "";
open $ResultsHandle, '<', \$return;
while (defined ($resultLine = <$ResultsHandle>)) {
    if ($resultLine =~ m/joe/) {
        $matchLines = $matchLines . "\t" . $resultLine;
    }
}
close($ResultsHandle);
print "Original string: \n$return\n";
print "Found these matching lines: \n$matchLines\n";

If you leave $ResultsHandle undefined before the open(), it will be filled in with a reference to the file handle. Because you were setting it to a string, open() presumed that it was supposed to be a symbolic reference to a variable instead --- not allowed under use strict.

Answer 3

The more succinct PBP way is to use open like so:

open my $ResultsHandle, '<', \$return;

This eliminates the need for that earlier "my $Resultshandle;" declaration and avoids incurring that strict warning that you ran into.

Answer 4

Change

my $ResultsHandle = "";

to

my $ResultsHandle;

Answer 5

Better result with split can be done by:

my $result="LINE1
line2
linE3
";
#attention, /^/m allows properly operate on multiline string using regex
#and ^ is character empty begin all lines
foreach my $resultLine (split /^/m, $result) {
    print $resultline;  #withount '\n' because it have got
    #some checks & operations
}

Answer 6

You can also use a regexp as an iterator:

my $data = q{Hello
This
Is
A
Test};

while( $data =~ /(.+)$/mg) {
    print "line is '$1'\n";
}

This is slightly less convoluted compared to using a filehandle that represents a string.