toolic hit the nail on the head, but you might choose a different delimiter so that it wouldn't be necessary to escape the forward slash, like this:
my $thing = 'foo/bar/goo';
( my $stuff ) = ( $thing =~
m{ # Quote-like characters are now {}.
^ # Match at the start of the string.
( [^/]+ ) # Capture everything in the set of all
# characters that are not '/'
}x # Close the regexp. x modifier allows
# freeform (as in non-significant
# whitespace).
);
print "$stuff\n";
The m{} brackets avoid the leaning toothpick syndrome in the original regexp. Of course if you were matching against a curly bracket the curly brackets wouldn't be all that wonderful as quote delimiters, but for this regexp they work out well. /x modifier added to allow comments and insignificant whitespace (it makes everything prettier).