- Updated solution.

1 files changed, 138 insertions, 107 deletions

diff --git a/challenge-112/colin-crain/perl/ch-1.pl b/challenge-112/colin-crain/perl/ch-1.pl
index 3a638cea0f..ff7a309d49 100644
--- a/challenge-112/colin-crain/perl/ch-1.pl
+++ b/challenge-112/colin-crain/perl/ch-1.pl
@@ -1,107 +1,138 @@
-#!/Users/colincrain/perl5/perlbrew/perls/perl-5.32.0/bin/perl

-#

-#       where-am-i-where-are-my-friends.pl

-#

-#         Canonical Path

-#         Submitted by: Mohammad S Anwar

-#         You are given a string path, starting with a slash ‘/'.

-# 

-#         Write a script to convert the given absolute path to the simplified

-#         canonical path.

-# 

-#         In a Unix-style file system:

-# 

-#         - A period '.' refers to the current directory

-#         - A double period '..' refers to the directory up a level

-#         - Multiple consecutive slashes ('//') are treated as a single slash '/'

-#         The canonical path format:

-# 

-#         - The path starts with a single slash '/'.

-#         - Any two directories are separated by a single slash '/'.

-#         - The path does not end with a trailing '/'.

-#         - The path only contains the directories on the path from the root

-#         directory to the target file or directory

-#  

-#         Example

-#             Input: "/a/"

-#             Output: "/a"

-# 

-#             Input: "/a/b//c/"

-#             Output: "/a/b/c"

-# 

-#             Input: "/a/b/c/../.."

-#             Output: "/a"

-# 

-#         method

-#             converting to a canonical path form is not quite as simple as

-#             restructuring dot file notaion into real directories and

-#             normalizing superfluous chaff such as '//', because a canonical

-#             path is always an absolute path and the relative path given may

-#             not be.

-# 

-#             Fortunately for us today we are defined as having been given an

-#             absolute path, sidestepping that mess. 

-# 

-#             However a canonical path also resolves soft links, which remains a 

-#             difficulty, as Perl is not a shell. There are ways involving a module

-#             to address this, but I'm going to assume this edge case is outside

-#             the scope of the problem.

-# 

-#

-#       © 2021 colin crain

-## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ##

-

-

-

-use warnings;

-use strict;

-use feature ":5.26";

-use feature qw(signatures);

-no warnings 'experimental::signatures';

-

-use Cwd qw( abs_path );

-

-

-

-sub canonical ($path) {

-    $path =~ s{/\.?/}{/}g;

-    $path =~ s{/$}{};

-    

-    my @parts = split '/', $path;

-    my $pos = 0;

-    while (++$pos < @parts) {   

-        if ($parts[$pos] eq '..') {

-            splice @parts, $pos-1, 2;

-            $pos -= 2;            

-        }

-    }

-    join '/', @parts;

-}

-

-# this will resolve relative paths, and soft links, from the cwd, which doesn't

-# really solve that problem in a general way. We need to `chdir` over to 

-# the place in question, which would need to both exist and have the right permissions. 

-# The whole thing is a bit of a mess, really, and I don't think that's what Mohammad is

-# asking of us. 

-

-sub canonical_softlinks ($path) {

-    chdir $path;

-    return abs_path( $path );

-}

-

-## resolving the link from d -> e

-## yields /Users/colincrain/a/b/c/e

-

-my $path = '../../a/b/c/f/../d';

-say canonical_softlinks( $path );

-

-

-

-use Test::More;

-

-is canonical("/a/"), "/a"             , 'ex-1';

-is canonical("/a/b//c/"), "/a/b/c"    , 'ex-2';

-is canonical("/a/b/c/../.."), "/a"    , 'ex-3';

-

-done_testing();

-

+#!/Users/colincrain/perl5/perlbrew/perls/perl-5.32.0/bin/perl
+#
+#       PWC 112 - TASK 1
+#
+#       where-am-i-where-are-my-friends.pl
+#
+#         Canonical Path
+#         Submitted by: Mohammad S Anwar
+#         You are given a string path, starting with a slash ‘/'.
+#
+#         Write a script to convert the given absolute path to the simplified
+#         canonical path.
+#
+#         In a Unix-style file system:
+#
+#         - A period '.' refers to the current directory
+#         - A double period '..' refers to the directory up a level
+#         - Multiple consecutive slashes ('//') are treated as a single slash '/'
+#         The canonical path format:
+#
+#         - The path starts with a single slash '/'.
+#         - Any two directories are separated by a single slash '/'.
+#         - The path does not end with a trailing '/'.
+#         - The path only contains the directories on the path from the root
+#         directory to the target file or directory
+#
+#         Example
+#             Input: "/a/"
+#             Output: "/a"
+#
+#             Input: "/a/b//c/"
+#             Output: "/a/b/c"
+#
+#             Input: "/a/b/c/../.."
+#             Output: "/a"
+#
+#         method
+#             converting to a canonical path form is not quite as simple as
+#             restructuring dot file notaion into real directories and
+#             normalizing superfluous chaff such as '//', because a canonical
+#             path is always an absolute path and the relative path given may
+#             not be.
+#
+#             Fortunately for us today we are defined as having been given an
+#             absolute path, sidestepping that mess.
+#
+#             However a canonical path also resolves soft links, which remains a
+#             difficulty, as Perl is not a shell. There are ways involving a module
+#             to address this, but I'm going to assume this edge case is outside
+#             the scope of the problem.
+#
+#
+#       © 2021 colin crain
+## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ##
+
+
+
+use warnings;
+use strict;
+use feature ":5.26";
+use feature qw(signatures);
+no warnings 'experimental::signatures';
+use Cwd qw( abs_path );
+
+
+sub canonical ($path) {
+    $path =~ s{//+}{/}g;
+    $path =~ s{/\./}{/}g;
+    $path =~ s{/$}{};
+
+    my @parts = split '/', $path;
+
+    my $pos = 0;
+    while ($pos < @parts) {
+        if ($parts[$pos] eq '..') {
+            if ($pos > 0) {
+                splice @parts, $pos-1, 2;
+                $pos -= 2;
+            }
+            else {
+                splice @parts, $pos, 1;
+                $pos--;
+            }
+        }
+        $pos++;
+    }
+    @parts = (undef, undef) unless scalar @parts;
+    unshift @parts, '' if $parts[0] ne '';
+    join '/', @parts;
+}
+
+## this will resolve relative paths, and soft links, with the Cwd package, which
+## doesn't really solve that problem in a general way. We need to `chdir` over to
+## the place in question, which would need to both exist and have the right
+## permissions. The whole thing is a bit of a mess, really, and I don't think
+## that's what Mohammad is asking of us.
+sub canonical_softlinks ($path) {
+    chdir $path;
+    return abs_path( $path );
+}
+
+## a solution using realpath from the system utilities
+## we still need to chdir down to root unless we want the cwd prepended to an assumed
+## relative path
+sub canon_sys ($path) {
+    my $cur = `pwd`;
+    chdir '/';
+    my $out = `realpath -m $path` ;
+    chomp $out;
+    chdir $cur;
+    return $out;
+}
+
+
+
+use Test::More;
+
+is canonical("/a/"), "/a"             , 'ex-1';
+is canonical("/a/b//c/"), "/a/b/c"    , 'ex-2';
+is canonical("/a/b/c/../.."), "/a"    , 'ex-3';
+is canonical('a/b/c//.//../d/'), "/a/b/d"    , 'hateful';
+is canonical("../../../b"), "/b"             , 'rogers bane';
+is canonical(".."), "/"             , 'no path';
+is canonical("/"), "/"             , 'no path2';
+
+
+is canon_sys("/a/"), "/a"             , 'sys-ex-1';
+is canon_sys("/a/b//c/"), "/a/b/c"    , 'sys-ex-2';
+is canon_sys("/a/b/c/../.."), "/a"    , 'sys-ex-3';
+is canon_sys('a/b/c//.//../d/'), "/a/b/d"    , 'sys-hateful';
+is canon_sys("../../../b"), "/b"             , 'sys-rogers bane';
+is canon_sys(".."), "/"             , 'sys-no path';
+is canon_sys("/"), "/"             , 'sys-no path2';
+
+
+done_testing();
+
+