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perl -T and #!/usr/bin/perl -T conflict

by ichimunki (Priest)
on Jan 24, 2001 at 23:22 UTC ( #54086=perlquestion: print w/replies, xml ) Need Help??

ichimunki has asked for the wisdom of the Perl Monks concerning the following question:

I have a script that has -T on the hashbang line. I normally call it using the Unix method ./ (having chmod 7**'ed it). No problem.

The same script generates a taint error at line 1 when executed using "perl". This stops the program before it gets started. Everything goes back to normal when using "perl -T" to execute. But this is less than ideal. I don't want everyone who might use the script to have to learn to use the -T switch when executing.

Is there a way to ensure taint checking without having to explicitly explain this to potential users?
  • Comment on perl -T and #!/usr/bin/perl -T conflict

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perl T-shirt and #!/usr/bin/perl -T conflict
by dws (Chancellor) on Jan 25, 2001 at 07:45 UTC
    When I first saw this thread in Newest Nodes, I misread it as
    perl T-shirt and #!/usr/bin/perl -T conflict
    (I'd recently seen jima's note about the nifty Camel T-shirt, and probably hadn't had enough sleep.)

    But I wonder, doesn't a t-shirt that reads

    #!/usr/bin/perl -w use strict;
    cover only two of the four most common bits of advice handed out here? Wouldn't a truly monastery-compliant t-shirt begin
    #!/usr/bin/perl -Tw use strict; use CGI; # don't reinvent the wheel
    And then, on the back
    (*)++ ( )-- ( )+= 0
      Unless things were very different back then, I'm wondering how ()+= 0 is monastary-compliant.

      Linux, sci-fi, and Nat Torkington, all at Penguicon 3.0
      perl -e 'print(map(chr,(0x4a,0x41,0x50,0x48,0xa)))'
Re: perl -T and #!/usr/bin/perl -T conflict
by rlk (Pilgrim) on Jan 24, 2001 at 23:54 UTC
    Here's the simple solution.
    #!/usr/bin perl -w print "Script started\n"; eval { exec("perl -wT $0") #Only works if taint mode off }; print "Now we're in taint mode!\n";
    Unfortunately, if your script is suid, this has a gaping security hole, as you've just executed an arbitrary program as root. (Was it /usr/bin/perl as you were expecting, or was it /home/l33t_hax0r/bin/perl? With an insecure $ENV{PATH}, you'll never know.)

    Here's a version that fixes that particular hole

    #!/usr/bin perl -w print "Script started\n"; eval { $ENV{PATH}, exec("/path/to/perl -wT $0") #Only works if ta +int mode off }; print "Now we're in taint mode!\n";
    Eliminating the "useless use of a hash element in void context" message is left as an exercise for the reader. (Hint: look at the is_tainted function example in perlsec)

    Ryan Koppenhaver, Aspiring Perl Hacker
    "I ask for so little. Just fear me, love me, do as I say and I will be your slave."

Re: perl -T and #!/usr/bin/perl -T conflict
by KM (Priest) on Jan 24, 2001 at 23:34 UTC
    I assume you mean the 'Too late for "-T" option at line 1.' error. This happens because you have run perl without -T, then when it examines the #! line and sees -T, it realizes you want tainting, but it is too late. You need to make sure -T is passed when using 'perl'. I know of no way around this, as opposed to aliasing 'perl' with 'perl -T' or some similar lunacy.


      Neat related idea (and you know, I have princepawn to thank for making me think about this in the first place) -- you could also have a batch file (as you explained in the CB, you're worried about porting to win32), that calls perl.exe -T %1 (or however that's done =), call it (say) perlrun.bat, stick it in your PATH, and call the script as perlrun

      Philosophy can be made out of anything. Or less -- Jerry A. Fodor

Re: perl -T and #!/usr/bin/perl -T conflict
by arturo (Vicar) on Jan 24, 2001 at 23:29 UTC

    I'd just chmod 0755 so they can all execute it via a simple /path/to/ , then tell 'em *NOT* to run it through the interpreter from the command-line unless they know what they're doing. The message you're getting is probably "Too late for -T switch". I don't think there is any way around this behavior, but if there is, I'm sure someone else who frequents this site does =)

    Philosophy can be made out of anything. Or less -- Jerry A. Fodor

Re: perl -T and #!/usr/bin/perl -T conflict
by japhy (Canon) on Jan 24, 2001 at 23:46 UTC

      <bad humour> If 'tain't perl, shouldn't that be alias taintperl 'ruby -T' ? </bad humour>


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