Perl: How to detect which file exists among foo.(txt|abc) - perl

Question

My perl script needs to detect the extension of an existing file and print out the filename. The input that specifies the filename with a vague extension would be in this format:
foo.(txt|abc)
and the script would print "foo.txt" if it exists. If foo.txt does not exist and foo.abc exists, then it would print "foo.abc."
How can I do this detection and printing of the correct existing file in a neat and clean way?
Thanks!

Answer 1

Actually, you've almost got the regular expression right there: the only thing you need to do is escape the . with a backslash (since . means "any character except the newline character" in regular expressions), and it would also help to put a ?: inside of the parentheses (since you don't need to capture the file extension). Also, ^ and $ denote markers for the beginning and the end of the string (so we're matching the entire string, not just part of a string...that way we don't get a match for the file name "thisisnotfoo.txt")
Something like this should work:
use strict;
use warnings;
my $file1="foo.txt";
my $file2="foo.abc";
my $file3="some_other_file";
foreach ($file1,$file2,$file3)
{
if(/^foo\.(?:txt|abc)$/)
{
print "$_\n";
}
}
When the above code is run, the output is:
foo.txt
foo.abc
Take a look at perldoc perlretut for more stuff about regular expressions.

Answer 2

You may want to look at glob, but you'd have to use a different syntax. The equivalent would be:
foo.{txt,abc}
See File::Glob for more information. Also note that this will return a list of all of the matches, so you'll have to do your own rules if it should prefer one when multiple exist.

Answer 3

sub text_to_glob {
my ($s) = #_;
$s =~ s/([\\\[\]{}*?~\s])/\\$1/g;
return $s;
}
my $pat = 'foo.(txt|abc)';
my #possibilities;
if (my ($base, $alt) = $pat =~ /^(.*\.)\(([^()]*)\)\z/s) {
#possibilities = glob(
text_to_glob($base) .
'{' . join(',', split(/\|/, $alt)) . '}'
);
} else {
#possibilities = $pat;
}
for my $possibility (#possibilities) {
say "$possibility: ", -e $possibility ? "exists" : "doesn't exist";
}
glob, but also see File::Glob
-e

Answer 4

use strict;
use warnings;
FILE:
for (glob "file.{txt,abc}") {
if (-f $_) {
print $_, "\n";
last FILE;
}
}