Or, to avoid accidents:

if ($args =~ /(?:\A|\s)-iL(?:\s+([^\s]+)|\s*\Z)/) {
  print "Found -iL, the value is ", (defined($1) ? "'$1'" : 'absent'),
+ "\n" ;
}
[download]

which:

• will not find -iL at the end of some word, eg Tref-iL. (Surprisingly there doesn't seem to be a cleaner way of expressing "whitespace or start of string".)
• uses [^\s] rather than \w -- assuming less about the value of the thing after -iL. (The original fragment used split(/\ /, ...), so strictly should use \ not \s... I have my poet's licence, if you want to see it.)
• will find a -iL even if it's the last thing in the $args, which may or may not be a good thing to trap as an error in the input.

Sadly, this doesn't look as pretty any more :-(

Oh. And FWIW, none of this will cope if the $arg string contains quoted elements -- something way smarter is required !