32

What's the best way to check if two paths are equal in Bash? For example, given the directory structure

~/
  Desktop/
    Downloads/ (symlink to ~/Downloads)
  Downloads/
    photo.png

and assuming that the current directory is the home directory, all of the following would be equivalent:

./                    and ~
~/Desktop             and /home/you/Desktop
./Downloads           and ~/Desktop/Downloads
./Downloads/photo.png and ~/Downloads/photo.png

Is there a native Bash way to do this?

James Ko
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  • Most of the answers (except mine) will break with bind mounts and things other than symlinks that can make two paths refer to the same thing. – Peter Cordes Nov 29 '15 at 08:05
  • Alternatively: https://stackoverflow.com/questions/284662/how-do-you-normalize-a-file-path-in-bash Related: https://unix.stackexchange.com/questions/206973/how-to-find-out-whether-two-directories-point-to-the-same-location – Ciro Santilli OurBigBook.com Jun 09 '18 at 19:31
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    re: @Ciro's links: [How do you normalize a file path in Bash?](https://stackoverflow.com/q/284662) will help you check for path equality like asked, but doesn't handle bind-mounts if you want to actually check if 2 paths are the same file/directory on disk. (Which is what the accepted answer here does.) [How to find out whether two directories point to the same location](https://unix.stackexchange.com/q/206973) has answers that do that, but the current accepted one is just path canonicalization. – Peter Cordes Jan 09 '21 at 01:35

5 Answers5

48

Bash's test commands have a -ef operator for this purpose

if [[ ./ -ef ~ ]]; then ...

if [[ ~/Desktop -ef /home/you/Desktop ]]; then ...

etc...

$ help test | grep -e -ef
      FILE1 -ef FILE2  True if file1 is a hard link to file2.
geirha
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    Nice! It looks like this method properly [compares device and inode numbers](http://linux.about.com/library/cmd/blcmdl1_test.htm) as well, so I'm accepting this answer. – James Ko Nov 29 '15 at 18:15
  • `if [ ./ -ef ~ ]; then` should be enough, test is synonymous to `[` – tesch1 Aug 23 '18 at 01:04
  • Confirmed, it works across bind mounts, making my `find -samefile` answer obsolete. – Peter Cordes Jan 09 '21 at 01:25
  • It helped me with windows git bashrc path logical operator comparision for cd-ing. Thanks. – ajay4q Feb 26 '22 at 21:15
6

You can use realpath. For example:

realpath ~/file.txt
Result: /home/testing/file.txt

realpath ./file.txt
Result: /home/testing/file.txt

Also take a look at a similar answer here: bash/fish command to print absolute path to a file

Community
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zedfoxus
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4

Native bash way:

pwd -P returns the physical directory irrespective of symlinks.

cd "$dir1"
real1=$(pwd -P)
cd "$dir2"
real2=$(pwd -P)
# compare real1 with real2

Another way is to use cd -P, which will follow symlinks but leave you in the physical directory:

cd -P "$dir1"
real1=$(pwd)
cd -P "$dir2"
real2=$(pwd)
# compare real1 with real2
Tom Zych
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  • This only works for symlinks. If the same filesystem is mounted at multiple points (e.g. `mount --bind /raid0/var-cache /var/cache`), then your best bet is to compare inodes. – Peter Cordes Nov 29 '15 at 07:37
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    This doesn't do quite what you want, since the first directory-change affects the interpretation of any relative path in the second one. To fix this, you should move the `cd` inside the command substitution (so it runs inside the subshell). – ruakh Nov 29 '15 at 08:15
  • @ruakh makes an excellent point that I'd overlooked. geirha's answer is also quite interesting. – Tom Zych Nov 29 '15 at 12:30
3

If you have coreutils 8.15 or later installed, you have a realpath command that fully normalizes a path. It removes any . and .. components, makes the path absolute, and resolves all symlinks. Thus:

if [ "$(realpath "$path1")" = "$(realpath "$path2")" ]; then
   echo "Same!"
fi
rob mayoff
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3

Methods based on resolving symlinks fail when there are other factors involved. For example, bind mounts. (Like mount --bind /raid0/var-cache /var/cache

Using find -samefile is a good bet. That will compare filesystem and inode number.

-samefile is a GNU extension. Even on Linux, busybox find probably won't have it. GNU userspace and Linux kernel often go together, but you can have either without the other, and this question is only tagged Linux and bash.)

# params: two paths.  returns true if they both refer to the same file
samepath() {
    # test if find prints anything
    [[ -s "$(find -L "$1" -samefile "$2")" ]]  # as the last command inside the {}, its exit status is the function return value
}

e.g. on my system:

$ find /var/tmp/EXP/cache/apt/archives/bash_4.3-14ubuntu1_amd64.deb  -samefile /var/cache/apt/archives/bash_4.3-14ubuntu1_amd64.deb 
/var/tmp/EXP/cache/apt/archives/bash_4.3-14ubuntu1_amd64.deb


$ stat {/var/tmp/EXP,/var}/cache/apt/archives/bash_4.3-14ubuntu1_amd64.deb
  File: ‘/var/tmp/EXP/cache/apt/archives/bash_4.3-14ubuntu1_amd64.deb’
...
Device: 97ch/2428d      Inode: 2147747863  Links: 1
...

  File: ‘/var/cache/apt/archives/bash_4.3-14ubuntu1_amd64.deb’
Device: 97ch/2428d      Inode: 2147747863  Links: 1

You can use find -L for cases where you want to follow symlinks in the final path component:

$ ln -s   /var/cache/apt/archives/bash_4.3-14ubuntu1_amd64.deb foo
$ find    /var/cache/apt/archives/bash_4.3-14ubuntu1_amd64.deb  -samefile foo
$ find -L /var/cache/apt/archives/bash_4.3-14ubuntu1_amd64.deb  -samefile foo
/var/cache/apt/archives/bash_4.3-14ubuntu1_amd64.deb

Obviously this works for paths which refer to directories or any type of file, not just regular files. They all have inode numbers.

usage:

$ samepath /var/cache/apt/  /var/tmp/EXP/cache/apt/  && echo true
true
$ ln -sf /var/cache/apt foobar
$ samepath foobar /var/tmp/EXP/cache/apt/  && echo true
true
samepath /var/tmp/EXP/cache/apt/ foobar   && echo true
true
samepath foobar   && echo true   # doesn't return true when find has an error, since the find output is empty.
find: `': No such file or directory

So find -L dereferences symlinks for -samefile, as well as for the list of paths. So either or both can be symlinks.

Peter Cordes
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    +1. Could you add some information about portability, though? (It doesn't look like `-samefile` is specified by POSIX?) – ruakh Nov 29 '15 at 08:12
  • @ruakh: oh right, it's a GNU extension, probably only found in GNU `find`. Obviously `bash` doesn't come with GNU find, but I think the `linux` tag made me leave out a mention of this. – Peter Cordes Nov 29 '15 at 08:17