Curious Symlink question

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

Replies are listed 'Best First'.
Re: Curious Symlink question by Roy Johnson (Monsignor) on May 02, 2005 at 22:56 UTC
What you've written suggests that you want a file to know what symlinks there are to it. It does not. For the other direction — determining where a symlink points — use readlink. Caution: Contents may have been coded under pressure.	[reply]
Re^2: Curious Symlink question by patrickrock (Beadle) on May 02, 2005 at 22:59 UTC
Roy, Yes, precisely. I wondered if there was a way for a file to know what symlink was originally. I thought maybe it got passed along or something. Sigh, I guessed not, but one can hope.	[reply]
Re^3: Curious Symlink question by Roy Johnson (Monsignor) on May 02, 2005 at 23:09 UTC
If you're calling the program using the symlink, you can use `__FILE__` (or, as the others have suggested, $0). That gives you the name of the program called, and it doesn't matter whether it's a symlink or a real file. If you're calling the program using the real file name, no. A file might have numerous symlinks to it, and it doesn't have any place to keep track of them. Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re^3: Curious Symlink question by ikegami (Patriarch) on May 02, 2005 at 23:01 UTC
You can, if you want the symlink used to start the Perl script currently being executed. It's in $0.	[reply]
Re: Curious Symlink question by eibwen (Friar) on May 02, 2005 at 22:45 UTC
Your post is a bit difficult to follow, but `$0` will return the name of the code as invoked. To illustrate: $ echo "#!/usr/bin/perl\nprint $0;" > tmp $ ln -s tmp temp $ ./temp ./temp UPDATE: Beware potential shell interpolation of `$0`. The ./tmp file should contain the follow two lines: `#!/usr/bin/perl -w print $0` [download]	[reply] [d/l] [select]
Re^2: Curious Symlink question by patrickrock (Beadle) on May 03, 2005 at 16:06 UTC
yes! brilliant. the $0 var worked just as you guys described. Sorry my question was confusing. Even apparently to myself. Thanks for your help, and if you want here is the longer story. Oracle applications 10.7 provides a way to feed arguments from oracle apps to a shell script. It works like this 1. Make your shell script with a .prog extenstion. so test.prog 2. make a symlink to a special oracle binary like so using the name of your .prog so: ln -s fnddescr test then define test in oracle. you call test from oracle, give it your arguments, and then oracle calls test which calls fnddescr which parses the oracle payload, and hands the arguments back to test.prog. we wanted to know if how fnddescr could know what called it. presumably they have something similiar to $0 again thanks for your help!	[reply]
Re: Curious Symlink question by tlm (Prior) on May 02, 2005 at 23:43 UTC
You may want to check out FindBin. It exports the following variables (quoting from the docs): `$Bin`: path to bin directory from where script was invoked `$Script`: basename of script from which perl was invoked `$RealBin`: `$Bin` with all links resolved `$RealScript`: `$Script` with all links resolved the lowliest monk	[reply]
Re: Curious Symlink question by cbrandtbuffalo (Deacon) on May 03, 2005 at 11:46 UTC
The brute-force approach would be to search your entire file system with something like merlyn's Find out where symlinks point, and find all the symlinks that expand to the original path you're looking for. Then you know who points to the original script. This would be feasible if you just needed to know at a point in time. Of course you probably wouldn't want to run it often.	[reply]


Keep It Simple, Stupid
	PerlMonks