You can place a copy of your perl's lib.pm into the directory where your debug versions of modules live. Then edit that lib.pm to remember the first path actually passed to use lib: 

my $sticky_dir;                                             # EDIT
sub import {
    shift;

    my %names;
    foreach (reverse @_) {
        my $path = $_;          # we'll be modifying it, so break the 
+alias
        $sticky_dir = $path unless $sticky_dir;             # EDIT
        if ($path eq '') {

    ...

    # remove trailing duplicates
    @INC = grep { ++$names{$_} == 1 } @INC;

    # put sticky dir up front                               # EDIT
    @INC = ($sticky_dir, grep { ! m{^$sticky_dir$} } @INC); # EDIT
    return;
}

[download]

See the lines marked with # EDIT. Make sure your directory is the first which gets into the private $sticky_dir variable. All subsequent calls to use lib will result in the directories being placed after the sticky directory:

#!/usr/bin/perl
BEGIN{                                  # necessary
    unshift @INC,'/home/shmem/tmp/foo'; # so 'use lib'
}                                       # gets my version

use lib "/home/shmem/tmp/foo";          # this dir is now sticky

BEGIN { 
    print "lib is ",$INC{"lib.pm"},$/;
}

use lib "/some/path";
BEGIN {
    print "\@INC after 'use lib \"/some/path\":\n";
    print "$_\n" for @INC;
}
use lib "/another/path";
BEGIN {
    print "\@INC after 'use lib \"/another/path\":\n";
    print "$_\n" for @INC;
}
__END__
lib is /home/shmem/tmp/foo/lib.pm
@INC after 'use lib "/some/path":
/home/shmem/tmp/foo
/some/path
/etc/perl
/usr/local/lib/perl/5.18.2
/usr/local/share/perl/5.18.2
/usr/lib/perl5
/usr/share/perl5
/usr/lib/perl/5.18
/usr/share/perl/5.18
/usr/local/lib/site_perl
.
@INC after 'use lib "/another/path":
/home/shmem/tmp/foo
/another/path
/some/path
/etc/perl
/usr/local/lib/perl/5.18.2
/usr/local/share/perl/5.18.2
/usr/lib/perl5
/usr/share/perl5
/usr/lib/perl/5.18
/usr/share/perl/5.18
/usr/local/lib/site_perl
.

[download]

update: Instead of the first BEGIN block, invoking a script like this 

perl -I/my/debug/directory script

[download]

prepends /my/debug/directory to @INC to have /my/debug/directory/lib.pm loaded at the first call to use lib inside the script - so you can switch on debugging without modifying the script at all.

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

In reply to Re: Containing 'use lib' statements in modules to their own namespace by shmem
in thread Containing 'use lib' statements in modules to their own namespace by lgp171188

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