How to check if two paths are equal in Bash?

问题:

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?

回答1:

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.

回答2:

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

回答3:

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

回答4:

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

回答5:

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.