Use of / when using cd

Question

I'm in my home directory on my mac:

$ pwd
/Users/lukas

When I cd around, I do not (and can't) start the path with /:

$ cd Documents/
/Users/lukas/Documents

$ cd /Documents
-bash: cd: /Documents: No such file or directory

Except when I'm in /:

$ pwd
/
$ cd Users
/Users

$ cd /Users
/Users

Why can I use / in front of the path when going from / to /Users but not in any subsequent levels? Is this specific to macOS or is this standard Unix behavior?

I think questions about relative and absolute paths have been asked befofre — adamczi, Nov 21 '18 at 14:20
@adamczi It is pretty obvious that OP does not know what a relative path is, or how its syntax is, thus he can't look it up. — RaidenF, Nov 21 '18 at 14:42
@K.Gkinis Which is not a reason for not closing as duplicate. It help askers to get good answers (assume answers are good) and answerers to maintain less versions of the same content. — user202729, Nov 21 '18 at 15:32
@K.Gkinis And, in a sense, that is a large part of the point of closing as a duplicate: people will ask questions in lots of different ways, so lots of questions (matching those ways) pointing to a single answer is a Good Thing. In cases like this (where an OP doesn't know the term to search for), closing-as-dupe is not a criticism of them, just the best way of handling the many way people ask questions. — TripeHound, Nov 21 '18 at 16:27
@adamczi They have been asked before (thank you for the links!) but my question and especially the great answers given here are way more detailed and explain the concept better than the answers you linked. Don't know if that matters for closing as duplicate, but might be a consideration. — LukasKawerau, Nov 22 '18 at 05:16
I totally understand that it's hard to search when you don't know what the term is, but I still stand for "this could be really easily searched for" - this returns that as the first result with even more complete answer. — adamczi, Nov 22 '18 at 10:40

score 45 · Accepted Answer · edited Nov 21 '18 at 05:39

45

This is standard Unix behaviour.

The / at the beginning of the path represents the root of the disk (or the start/uppermost level of the filesystem tree). As Documents is not off the root, /Documents can't be found.

/Users is off the root directory, so this problem does not occur.

You could use cd /Users/lukas/Documents to change to that path.

Alternatively, you could use relative addressing. Unix based filesystems have 2 special directories:

. which means "this directory",
.. which means the parent directory.

If you are in /Users/lukas, cd ./Documents would take you to the correct place.

Let's assume you were in /Users/Lukas/Documents and wanted to go to /Users/Janes/Documents, you could issue a command cd ../../Janes/Documents - using .. would take you back a level - so you would do it twice, before going into the new relative path.

edited Nov 21 '18 at 05:39

Kamil Maciorowski

74,068

answered Nov 21 '18 at 05:03

davidgo

70,654

1

Note: as @davidgo said, when in Users/lukas, cd Documents calls for the relative path; cd /Users/Lukas/Documents calls for the absolute path (which would be working whatever repertory you are in when calling this command). – Shan-x Nov 21 '18 at 10:22
1

While the question is about a Mac, which is a Unix system, this is also standard MS-DOS/Windows behavior (replacing / with \\) since DOS borrowed it (through a long, convoluted history) from Unix. – FreeMan Nov 21 '18 at 15:26
2

Also depending on the shell you use, cd $HOME/Documents or cd ~/Documents would also work. The shell variable HOME (accessed with $HOME) is the usual storage location for your home directory (~ being a special alias for $HOME). – pboss3010 Nov 21 '18 at 16:00

score 13 · Answer 2 · answered Nov 21 '18 at 13:36

/Users/lukas is an "absolute" path. The leading / represents the root directory of your filesystem.

lukas is a "relative" path. As it is not anchored to the root, it means "look for this in the current directory". Unless the current directory is /Users (or some other directory with a lukas in it), this will fail.

So, let's explore your examples, assuming you're in /Users/lukas:

$ cd Documents/
/Users/lukas/Documents

Relative path given => change to the directory "Documents" that's inside /Users/lukas.

$ cd /Documents
-bash: cd: /Documents: No such file or directory

Absolute path given => change to the directory /Documents.

$ pwd
/

This shows that you've now changed the working directory to the root directory, / (though the cd command to do this was not shown).

$ cd Users
/Users

Relative path given => change to the directory "Users" that's inside /.

$ cd /Users
/Users

Absolute path given => change to the directory /Users.

The key each time is that leading /. With it, the path is absolute. Without it, the path is relative. This rule is unambiguous because all absolute paths begin with / (because the root directory is always called /).

Here's some pseudocode loosely describing that algorithm:

MakePathAbsolute(path):
   if <path> starts with '/'
      return <path>
   else
      return <current directory>/<path>

The argument you pass to cd goes through this algorithm; the directory you end up changing to is the path that the algorithm returns.

Use of / when using cd

2 Answers2