Re: What script is this, and where is it? (Re: who am I?)

[AZed]

All of those mechanisms break if the script is being called by a symlink, and particularly so if nested symlinks are involved. You need to readlink($0) if (-l $0) first, and then check, and even then, it won't give you the same output as FindBin::RealBin.

Create the following directory structure in /var/tmp. Set up directories as follows (you'll need root for /usr/local/bin, so feel free to make the last step anywhere else in your path that you'd like):

cd /var/tmp
mkdir mydir
mkdir datadir
mkdir otherdir
cd otherdir
ln -s ../mydir symdir

Now take the following code and put it in /var/tmp/mydir/myname.pl:

#!/usr/bin/perl

use strict;
use warnings;

use FindBin;
use File::Basename qw( dirname );
use File::Spec::Functions qw( rel2abs );

my $name = $0;
$name = readlink($name) if(-l $name);

print "Finding a data path:\n\n";
print 'dirname($name):',dirname($name),"/../datadir\n";
print 'dirname(rel2abs($name)):',dirname(rel2abs($name)),"/../datadir\
+n";
print 'dirname($0):',dirname($0),"/../datadir\n";
print 'dirname(rel2abs($0)):',dirname(rel2abs($0)),"/../datadir\n";
print '$FindBin::RealBin:',$FindBin::RealBin,"/../datadir\n";

Symlink /var/tmp/symdir/myname.pl to /usr/local/bin/myname (or somewhere else on your path, if you can't or don't want to tamper with a system directory). Run 'myname'. You get:

Finding a data path:

dirname($name):/var/tmp/otherdir/symdir/../datadir
dirname(rel2abs($name)):/var/tmp/otherdir/symdir/../datadir
dirname($0):/usr/local/bin/../datadir
dirname(rel2abs($0)):/usr/local/bin/../datadir
$FindBin::RealBin:/var/tmp/mydir/../datadir

Only FindBin correctly points you to the correct data directory location.

Frankly, even without symlink forests, FindBin is more readable, though.

[ikegami]

All of those mechanisms break if the script is being called by a symlink, and particularly so if nested symlinks are involved. You need to readlink($0) if (-l $0) first,

Agreed.

Only FindBin correctly points you to the correct data directory location.

That's wrong.

/var/tmp/otherdir/symdir/../datadir

is the same directory as

/var/tmp/mydir/../datadir

so you demonstrated that working with readlinked $0 works.

even then, it won't give you the same output as FindBin::RealBin.

Doesn't matter.

FindBin is more readable, though.

What good is readable if it doesn't work as well. And I don't see how dirname($script_qn) is less readable than $FindBin::RealBin.

[AZed]

Edit: claims withdrawn. See below. Original message preserved below the jump.

Read more... (2 kB)

[ikegami]

*cough* ... look again.

/var/tmp/otherdir/symdir/../datadir' => '/var/tmp/otherdir/datadir'

I read it fine the first time.

/var/tmp/otherdir/symdir/../datadir

is equivalent to

/var/tmp/datadir

and not equivalent to

/var/tmp/otherdir/datadir

In "/var/tmp/otherdir/symdir/../datadir", the ".." is that of "mydir" which is a hard link to "/var/tmp".

Do like I did and test before contradicting someone.

$ cd /var/tmp
$ mkdir mydir
$ mkdir datadir
$ mkdir otherdir
$ touch mydir/in_mydir
$ touch datadir/in_datadir
$ touch otherdir/in_otherdir
$ cd otherdir
$ ln -s ../mydir symdir
$ ls /var/tmp/otherdir/symdir/../datadir
in_datadir
$ perl -le'opendir $dh, $ARGV[0] or die; print for grep /in/, readdir 
+$dh' /var/tmp/otherdir/symdir/../datadir
in_datadir