$ cat t.pl
use strict; use warnings;

while (<DATA>) {
    if (m".*?/(.*?)/" and $1 !~ m"gallery"i) {
        print "Match: $_";
    }
    else {
        print "No match: $_";
    }
}
__DATA__
foo bar/baz/boffo
bar foo/gallary/gallery
bim bam/gallery/blam/blim
arg blarg/gallery/flarg

$ perl t.pl
Match: foo bar/baz/boffo
Match: bar foo/gallary/gallery
No match: bim bam/gallery/blam/blim
No match: arg blarg/gallery/flarg