I had seen the "-s" option before, when reading perlrun, but had never tried using it till seeing your post. From what I can tell (on macosx 10.4.6, perl 5.8.6), it seems to work only if the script is stored in a file, and has a shebang line with this option flag -- and even then, it doesn't seem to work as advertised, unless the script is executable (runnable without passing it as an arg to "perl"):

$ perl -s -foo=bar -e 'print $foo,$/ if $foo'
Unrecognized switch: -foo=bar  (-h will show valid options).

# (and similarly with other arrangements of these args)


$ cat junk.pl
#!/usr/bin/perl -s

print "$foo\n" if $foo;

$ perl junk.pl

$ perl junk.pl -foo
1

$ perl junk.pl -foo=bar
1

# (I thought that should have printed "bar", but
# there must be some logical reason why it didn't.)


$ chmod +x junk.pl
$ junk.pl

$ junk.pl -foo
1

$ junk.pl -foo=bar
bar

# at last!
[download]

So -s is just not suitable for use with a one-liner script on the command line. Oh well. At least there are other ways of doing this sort of thing (as indicated by earlier replies).

UPDATE: Turns out the one-liner command-line script approach actually does work if you do it like this:

$ perl -se 'print "$foo\n" if $foo' -- -foo
1

$ perl -se 'print "$foo\n" if $foo' -- -foo=bar
bar
[download]

(thanks to blockhead for pointing this out to me.) There was something about the double-dash arg in the perlrun description of "-s", but it didn't seem to apply to this facet of perl's behavior.