Making Perl script *run itself* with flags

Question

I'm very new to Perl, and have recently encountered the following problem. My Perl code must all reside within a single file (it's being called by another program I have no control of). I now wish to make the script run with a flag (e.g., perl myscript.pl -T for taint mode), although it is initially called without the flag. How can I do that, i.e., how do I "set the flag" from within the Perl file?

One idea that I've had is to make the file launch itself again (after being called without flags), this time with the -T flag (by issuing a shell command such as system($^X, "myscript.pl -T", @ARGS);). Would that work? Any better ideas?

Archaimbaud

if you control myscript.pl you can set taint mode by altering your shebang line to include -T e.g. #!/usr/bin/env perl -T – Casualty

What command is used to invoke the script in the other program? If it's something like /path/to/myscript.pl, you can simply add -T to the shebang line. – Symploce

a -T in the shebang line doesn't necessarily enable taint mode -- if the script is invoked with perl from the shell without -T, you get a fatal error – Mesquite

Still, putting -T in the shebang is the simplest solution. It'll either work or your script won't start, telling you to try a more complex workaround. – Visible

@ThisSuitIsBlackNot, unfortunately I have no control over the program that invokes my script, otherwise it would've been too easy and not too interesting :) – Archaimbaud

@Archaimbaud That's not what I said. I asked how the other program invokes your script. If it calls /path/to/myscript.pl from a shell, for example, you can add -T to the shebang line in myscript.pl to enable taint mode; if it calls perl /path/to/myscript.pl, for example, adding -T to the shebang line will cause an error as mob points out. – Symploce

Answer 1

I think you're on the right track. You can make use of the $^{TAINT} variable, and exec instead of system:

exec($^X, $0, '-T', @ARGV) if $^{TAINT} < 1;

This won't work in all cases. For one thing, you'll lose some other command line switches that your script might initially be called with:

perl -I/path/to/some/more/libs -w -MNecessary::Module myscript.pl ...

There are some workarounds to some of these (use warnings or add -w switch to your exec statement above, analyze @INC and %INC to determine what -I and -M switches were added) but the more you can learn about exactly how your script is called, the more you can figure out what workarounds you need to worry about.

---

Depending on the ... group dynamics in play here, another approach is to exercise some indirect control of the calling program. Go ahead and put -T on the shebang line as @Hunter McMillen and @ThisSuitIsBlackNot suggest, wait for a bug report, and then diagnose the problem as "program not invoked with -T switch" ...

Mesquite

Unfortunately, this doesn't seem to work for me, most likely due to the issues you've mentioned. Putting the -T on the shebang line produces the following error: "-T" is on the #! line, it must also be used on the command line – Archaimbaud