Why does Perl file test operator "-l" not detect symlinks? - perl

Question

Why does the Perl file test operator "-l" fail to detect symlinks under the following conditions?
System Info
john#testbed-LT:/temp2/test$ uname -a
Linux Apophis-LT 4.13.0-37-generic #42-Ubuntu SMP Wed Mar 7 14:13:23 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
john#testbed-LT:/temp2/test$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 17.10
Release: 17.10
Codename: artful
Perl Info
john#testbed-LT:/temp2/test$ perl -v
This is perl 5, version 26, subversion 0 (v5.26.0) built for x86_64-linux-gnu-thread-multi (with 56 registered patches, see perl -V for more detail)
Test Resources
john#testbed-LT:/temp2/test$ touch regular_file
john#testbed-LT:/temp2/test$ mkdir dir
john#testbed-LT:/temp2/test$ ln -s regular_file symlink
john#testbed-LT:/temp2/test$ ls -al
total 12
drwxrwxr-x 3 john john 4096 May 6 02:29 .
drwxrwxrwx 6 john john 4096 May 6 02:29 ..
drwxrwxr-x 2 john john 4096 May 6 02:29 dir
-rw-rw-r-- 1 john john 0 May 6 02:29 regular_file
lrwxrwxrwx 1 john john 12 May 6 02:29 symlink -> regular_file
Script Containing Failing "-l" Operator
john#testbed-LT:/temp2/test$ cat ~/.scripts/test.pl
#!/usr/bin/perl
use strict;
use warnings;
use Cwd 'abs_path';
my $targetDir = "/temp2/test";
opendir(DIR, $targetDir) || die "Can't open $targetDir: $!";
while (readdir DIR) {
my $file = "$_";
if($file =~ m/^\.{1,2}/) {
next;
}
$file = abs_path($file);
if(-l "$file") {
print "Link: $file\n";
}
elsif(-d "$file") {
print "Dir: $file\n";
}
elsif(-f "$file") {
print "File: $file\n";
}
else {
print "\n\n *** Unhandled file type for file [$file]!\n\n";
exit 1;
}
}
closedir(DIR);
Script Output
john#testbed-LT:/temp2/test$ perl ~/.scripts/test.pl
File: /temp2/test/regular_file
Dir: /temp2/test/dir
File: /temp2/test/regular_file
Problem I'm Trying to Solve
Note in the above output that the symlink (named "symlink") is not listed while the file, "regular_file," is listed twice (I want "symlink" listed -- the actual link and not the file it points to).
When I change ... if(-l "$file") ... to ... if(lstat "$file") ... in the script, again "symlink" is not listed while "regular_file" is listed twice, but they are being listed from within the block meant to catch symlinks, i.e.:
john#testbed-LT:/temp2/test$ perl ~/.scripts/test.pl
Link: /temp2/test/regular_file
Link: /temp2/test/dir
Link: /temp2/test/regular_file
Goal
The output I'm trying to achieve (which is faked below -- not actually generated by the script, but by hand) is:
john#testbed-LT:/temp2/test$ perl ~/.scripts/test.pl
File: /temp2/test/regular_file
Dir: /temp2/test/dir
Link: /temp2/test/symlink
...but not necessarily in that order (I don't care about the order of the listing).
Why is the above-shown script not achieving the above-stated goal (why is the "-l" operator not working)?

Answer 1

perldoc Cwd:
abs_path
my $abs_path = abs_path($file);
Uses the same algorithm as getcwd(). Symbolic links and relative-path components ("." and "..") are resolved to return the canonical pathname, just like realpath(3). On error returns undef, with $! set to indicate the error.
(Emphasis mine.)
If you want to see symlinks, don't use abs_path.
What you want to do instead is
$file = "$targetDir/$file";
i.e. prepend the name of the directory you read $file from.
Additional notes:
opendir(DIR, $targetDir) || die "Can't open $targetDir: $!";
while (readdir DIR) {
my $file = "$_";
should be
opendir(my $dh, $targetDir) || die "Can't open $targetDir: $!";
while (my $file = readdir $dh) {
Why use bareword filehandles when you can just use normal variables (that are scoped properly)?
There's no reason to quote "$_" here.
Why first assign to $_ when you're just going to copy the string to $file in the next step?

Answer 2

Note in the above output that the symlink (named "symlink") is not listed while the file, "regular_file," is listed twice
Yeah, because you used abs_path to turn symlink into /temp2/test/regular_file. Get rid of that line.
By the way, you are missing
$file = "$targetDir/$file";
The only reason your program worked without it is because $targetDir happened to be the current work directory.