What is the significance of -T or -w in #!/usr/bin/perl?

perl shebang taint
vijay picture vijay · Jun 29, 2012 · Viewed 14.7k times · Source

I googled about #!/usr/bin/perl, but I could not find any satisfactory answer. I know it’s a pretty basic thing, but still, could explain me what is the significance of #!/usr/bin/perl in Perl? Moreover, what does -w or -T signify in #!/usr/bin/perl? I am a newbie to Perl, so please be patient.

Answer

Richard Huxton picture Richard Huxton · Jun 29, 2012

The #! is commonly called a "shebang" and it tells the computer how to run a script. You'll also see lots of shell-scripts with #!/bin/sh or #!/bin/bash.

So, /usr/bin/perl is your Perl interpreter and it is run and given the file to execute.

The rest of the line are options for Perl. The "-T" is tainting (it means input is marked as "not trusted" until you check it's format). The "-w" turns warnings on.

You can find out more by running perldoc perlrun (perldoc is Perl's documentation reader, might be installed, might be in its own package).

For scripts you write I would recommend starting them with:

#!/usr/bin/perl
use warnings;
use strict;

This turns on lots of warnings and extra checks - especially useful while you are learning (I'm still learning and I've been using Perl for more than 10 years now).

Related questions

What should I use for a Perl script's shebang line?

Which of these is better or faster to use as the shebang line for a Perl script? #! perl #! perl.exe #! fullpath/perl(/perl.exe) #! partialpath/perl(/perl.exe) And, when using #!perl, when it works on a particular system, how …

Read More
Why should the shebang line always be the first line?

I have a simple perl script as below: #!/usr/bin/perl use strict; use warnings; print "hello world!\n"; I can execute this script as below: >temp.pl hello world! > If I add some comments like this: #this …

Read More
Find size of an array in Perl

I seem to have come across several different ways to find the size of an array. What is the difference between these three methods? my @arr = (2); print scalar @arr; # First way to print array size print $#arr; # Second way to …

Read More