Modifying %ENV From The Shebang Line

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

Replies are listed 'Best First'.
Re: Modifying %ENV From The Shebang Line by ikegami (Patriarch) on Dec 17, 2007 at 23:39 UTC
First, what's with `env` all over the place? Not only is it useless, I think it's actually hurting here. You're asking it to locate the program `LD_LIBRARY_PATH=/my/lib`. Secondly, perlrun doesn't mention `#!/bin/sh -- -- perl --` but it does mention `#!/bin/sh -- # -- perl --` Unfortunately, that doesn't work with my `sh`. However, it's easy to work around that using `-x`. `#!/bin/sh eval 'MYTESTVAR=/my/lib exec /usr/bin/perl -x -S $0 ${1+"$@"}' if $runningUnderSomeShell; #!perl print "[", $ENV{MYTESTVAR}, "]\n";` [download]	[reply] [d/l] [select]
Re^2: Modifying %ENV From The Shebang Line by williams (Beadle) on Dec 17, 2007 at 23:55 UTC
Well, that's good enough for the front burner, i.e., that works great! I'll press on with `-x`. You're right about `perlrun`, though it doesn't matter. My code was right; my post was wrong, and I'll correct it. Thanks to all who replied. I've now been made whole by PerlMonks yet again. Jim	[reply] [d/l] [select]
Re: Modifying %ENV From The Shebang Line by philcrow (Priest) on Dec 17, 2007 at 22:27 UTC
Could you use a dummy script to launch the actual one? `#!/bin/bash export envar=value /path/to/actual/perl/script` [download] Phil The Gantry Web Framework Book is now available.	[reply] [d/l]
Re^2: Modifying %ENV From The Shebang Line by williams (Beadle) on Dec 17, 2007 at 22:41 UTC
That was also one of the solutions I posted. It does indeed work, but it seems crufty. For every Perl hook script I write, I've got to write a shell layer to kick it off. The layers could probably be symbolic links to a common script. If that's the best I can do, I can live with it. I just thought there was a better way, given the sneaky shebangs in `perlrun`. Thanks, Jim	[reply] [d/l]
Re^3: Modifying %ENV From The Shebang Line by halley (Prior) on Dec 18, 2007 at 14:11 UTC
One environment-fixing wrapper, as shown, but taking an argument that specifies which perl hook script to be run. `#!/bin/bash export LD_LIBRARY_PATH=... export HOOKS_PATH=/path/to/svn/hooks [ -f $HOOKS_PATH/$1 ] && perl $HOOKS_PATH/$1` [download] -- `[ e d @ h a l l e y . c c ]`	[reply] [d/l]
Re: Modifying %ENV From The Shebang Line by shmem (Chancellor) on Dec 17, 2007 at 23:39 UTC
`#!/usr/bin/perl unless ($ENV{FOO} =~ /fitzblorf/) { $ENV{FOO} = 'fitzblorf'; exec $0, @ARGV; }` [download] --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l]
Re^2: Modifying %ENV From The Shebang Line by ikegami (Patriarch) on Dec 17, 2007 at 23:43 UTC
That would need to be wrapped in a `BEGIN` block since it needs to be executed before a `use` statement.	[reply] [d/l] [select]
Re^3: Modifying %ENV From The Shebang Line by shmem (Chancellor) on Dec 17, 2007 at 23:46 UTC
Of course, but that would be advanced usage... if you do such bold stuff as loading modules, it would be required, yes ;-) --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply]
Re^4: Modifying %ENV From The Shebang Line by djp (Hermit) on Jul 07, 2010 at 02:55 UTC
Re: Modifying %ENV From The Shebang Line by eserte (Deacon) on Dec 17, 2007 at 22:52 UTC
I tried the first shebang line on my FreeBSD system, and it also failed. From looking at the truss output, it seems that the system uses execve(2) to call the shebang interpreter. So I looked at the execve manpage and found this paragraph: An interpreter file begins with a line of the form: #! interpreter arg When an interpreter file is execve'd, the system actually execve's the specified interpreter. If the optional arg is specified, it becomes the first argument to the interpreter, and the name of the originally execve'd file becomes the second argument; otherwise, the name of the originally execve'd file becomes the first argument. The original argu- ments are shifted over to become the subsequent arguments. The zeroth argument is set to the specified interpreter. Note: it's arg (singular). The manpage claims that this is POSIX standard, so it might apply to Linux, too.	[reply]
Re^2: Modifying %ENV From The Shebang Line by williams (Beadle) on Dec 17, 2007 at 23:28 UTC
Maybe that explains some of the results I've seen, where it appears everything after `interpreter` is glommed into a single argument. I'm now left with attempts like the following, which just churn the CPU and never start Perl. `#!/bin/bash eval 'LD_LIBRARY_PATH=/my/lib /usr/bin/perl /the/script' if $runningUnderSomeShell; warn "$ENV{LD_LIBRARY_PATH}\n";` [download] Again, this is based on `perlrun`, though I'm obviously doing something wrong. Thanks, Jim	[reply] [d/l] [select]
Re: Modifying %ENV From The Shebang Line by ikegami (Patriarch) on Dec 17, 2007 at 22:25 UTC
Why? Why not just use `#!/usr/bin/perl BEGIN { $ENV{LD_LIBRARY_PATH} = '/my/lib'; } ...` [download]	[reply] [d/l]
Re^2: Modifying %ENV From The Shebang Line by moritz (Cardinal) on Dec 17, 2007 at 22:33 UTC
Because, from the OP's description, perl doesn't load at all without the proper environment variables. So any adjustment to the environemnt must be made before perl starts.	[reply]
Re^2: Modifying %ENV From The Shebang Line by williams (Beadle) on Dec 17, 2007 at 22:35 UTC
That was the last of the solutions I posted. I get unresolved references from the `use` lines of the Subversion modules at startup. Everything works fine when `$LD_LIBRARY_PATH` includes where those libraries are installed. Thanks, Jim	[reply] [d/l] [select]
Re: Modifying %ENV From The Shebang Line by graff (Chancellor) on Dec 17, 2007 at 23:01 UTC
Have you tried (would it be suitable to use) the `-I/lib/path` option on the perl script's shebang line? `#!/usr/bin/perl -I/path/containing/my_modules use My::Module; # should load /path/containing/my_modules/My/Module. +pm` [download] This has always worked for me... UPDATE: Sorry, I see that I have misunderstood the question. Having checked the man page for "env", I would have expected the use of `LD_LIBRARY_PATH=/some/path` to work. Then again, I'm looking at a freebsd man page for this utility, and it looks like its behavior may differ according to your OS (in particular, "env"s behavior changed between freebsd 5.6 and 6.0, for example...) Maybe you need to use "/usr/bin/env -S ..." to get things to work as expected? (Maybe the "-S" option is peculiar to freebsd? I don't know.)	[reply] [d/l] [select]
Re^2: Modifying %ENV From The Shebang Line by williams (Beadle) on Dec 17, 2007 at 23:43 UTC
Subversion starts the hook script, and forces a particular command line syntax that doesn't include Perl's `-I`. However, I could use the `lib` pragma to get the same effect, and I am doing that. Somehow, though, it's not enough. I need `$LD_LIBRARY_PATH` also set before Perl starts or I get either an unresolved reference or a core dump from within the Subversion API. Thanks, Jim	[reply] [d/l] [select]
Re: Modifying %ENV From The Shebang Line by educated_foo (Vicar) on Dec 17, 2007 at 23:38 UTC
The "-- perl --" bit is just for Emacs's benefit, so you should try leaving it off (you can always use a local variables section at the end instead).	[reply]
Re^2: Modifying %ENV From The Shebang Line by ikegami (Patriarch) on Dec 17, 2007 at 23:42 UTC
That's not true. Perl needs it or else it will run the #! line when it notices "perl" isn't present in it.	[reply]
Re^3: Modifying %ENV From The Shebang Line by educated_foo (Vicar) on Dec 17, 2007 at 23:59 UTC
I stand corrected. I had forgotten (or maybe never read) that part. The full details in perlrun are much too long to quote, but here's one relevant passage: If the #! line does not contain the word "perl", the program named after the #! is executed instead of the Perl interpreter. This is slightly bizarre, but it helps people on machines that don't do #!, because they can tell a program that their SHELL is /usr/bin/perl, and Perl will then dispatch the program to the correct interpreter for them.	[reply]


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