Moreover, you probably don't want to remove a dot from somewhere further inside the string, only the starting one. You can add ^ to the regex, it only matches at the beginning of the string.

The final g means "global", it will remove all the occurrences of the pattern. As we only want to remove a single occurrence, we don't need it.

$file =~ s{^\.}{};
[download]

if you want to use the regex be sure to use an anchor to just remove a dot in the beginning of the string:  /^\./ being the dot a special regex char you need to escape it.

For a more robust solution use File::Spec file_name_is_absolute and rel2abs

# something like..

$path = File::Spec->rel2abs( $path ) unless File::Spec->file_name_is_a
+bsolute( $path )
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L*

Note that the rel2abs approach will only give the same result if / is the CWD. Otherwise it's a different result:

#!/usr/bin/env perl
use strict;
use warnings;
use File::Spec;

chdir '/tmp';
my $path = './root/git/common/crt_del/cert/DEFAULT.pem';

$path = File::Spec->rel2abs ($path)
  unless File::Spec->file_name_is_absolute ($path);
print "$path\n";
[download]

---

🦛

You will get better answers if you provide us with more context around your problem. After reading your question, my spidey-sense is going off. Forgive me for making a wild guess, but are you a Perl novice tasked with maintaining a script originally written by an experienced Perl programmer?

Is the my $file = shift; part of a subroutine? If so, show us the complete subroutine and where it is being called. Do you understand how the unwanted "." got there in the first place? Are you certain it needs to be removed? Instead of removing it in the subroutine, does it make more sense to ensure it isn't passed to the subroutine in the first place?

Firstly, I agree with others that it would be preferable to deal with the problem at the source, rather than fixing it within your code. It's entirely possible that you'll need to repeat exactly the same fix in multiple scripts, modules or subroutines.

If that's not possible, it may be insufficient to just add a ^ anchor and remove the g option. What about hidden files (e.g. .bashrc) or places where intentionally specifying the current directory is necessary. You may need something closer to

s{^[.](?=/root(?:/|$))}{}
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Consider this SSCCE:

#!/usr/bin/env perl

use strict;
use warnings;

use Test::More;

my @tests = (
    [qw{./root /root}],
    [qw{./root/ /root/}],
    [qw{./root/xyz /root/xyz}],
    [qw{./root_plus ./root_plus}],
    [qw{./not_root/ ./not_root/}],
    [qw{./script_not_in_path.pl ./script_not_in_path.pl}],
    [qw{.hidden .hidden}],
);

plan tests => 0+@tests;

for my $test (@tests) {
    my $file = $test->[0];
    $file =~ s{^[.](?=/root(?:/|$))}{};
    is $file, $test->[1];
}
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Output:

1..7
ok 1
ok 2
ok 3
ok 4
ok 5
ok 6
ok 7
[download]

That's just an example. Modify the test cases to better reflect your real data.

$file =~ s{.}{}g does not do what you say. . means "a character that's not a line feed", so that removes every character that's not a line feed from the string in $file.