Shebang

You know that you can turn warnings on with -w on the command line. You can also turn them on within the script itself. For that matter, you can give perl any command line option within the script itself. For example:

perl script.pl hello

to execute this:

#!perl -w

@input=@ARGV;

$outfile='outfile.txt';
open OUT, ">$outfile" or die "Can't open $outfile for write:$!\n";

$input2++;
$delay=2 if $input[0] eq 'sleep';

sleep $delay;

print "The first element of \@input is $input[0]\n";
print OUY "Slept $delay!\n";

has the same effect as:

perl -w script.pl hello

It may be more convenient for you to put the flag inside the script. It doesn't have to be just -w , it can be any argument Perl supports. Run

perl -h

for a full list.

The first line, #!perl -w is the shebang line. This is derived from UNIX, where Perl was first developed. UNIX systems make a script executable by changing an attribute. The operating system then loads the file and works out how to execute it -- in this case by looking at the first line, then loading the perl interpreter. Windows systems know that all files with a certain extension must be passed to a certain program for execution, eg all .bat files are passed to command.com, and all .xls files are passed to Excel. The point of all this being that you don't need a shebang line, but it doesn't hurt.