Are two files hardlinked?

Question

How can I tell if two files are hard-linked from the command line? e.g. something link this:

$ ls
fileA fileB fileC

$ is-hardlinked fileA fileB
yes

$ is-hardlinked fileA fileC
no

score 46 · Accepted Answer · edited Apr 13 '17 at 12:36

46

On most filesystems¹, a file is uniquely determined by its inode number, so all you need to check is whether the two files have the same inode number and are on the same filesystem.

Ash, ksh, bash and zsh have a construct that does the check for you: the file equality operator -ef.

[ fileA -ef fileB ] && ! [ fileA -ef fileC ]

For more advanced cases, ls -i /path/to/file lists a file's inode number. df -P /path/to/file shows what filesystem the file is on (if two files are in the same directory, they're on the same filesystem). If your system has the stat command, it can probably show the inode and filesystem numbers (stat varies from system to system, check your documentation). If you want a quick glance of hard links inside a directory, try ls -i | sort (possibly piped to awk).

¹ _{All native unix filesystems, and a few others such as NTFS, but possibly not exotic cases like CramFS.}

edited Apr 13 '17 at 12:36

Community

1

answered Nov 07 '11 at 22:58

Gilles 'SO- stop being evil'

829,060

And definitely not on anything FAT-based, where it would be detected as a "cross-linked" file. – Ignacio Vazquez-Abrams Nov 08 '11 at 00:16
7

Note that fileA -ef fileB also returns 0 (success) if fileA is a symlink to fileB, or vice versa, or they both link to the same file. – janmoesen Nov 08 '11 at 16:50
how do you actually run the command you suggested? I tried [ .bashrc -ef .bash/.bashrc ] and variations of this but it didn't really work. – Charlie Parker Jun 15 '14 at 04:33
@CharlieParker [ .bashrc -ef .bash/.bashrc ] is correct. Without context, of course, I have no idea why it “didn't really work” — you could be comparing the wrong files, you could be not checking the outcome correctly, you could be using a shell without -ef, ... – Gilles 'SO- stop being evil' Jun 15 '14 at 10:49
the thing I still find confusing is that I am used to giving commands in my terminal with a format like CMD [options] arg1 arg2 ... argN but this one seems to violate that format. I don't even know how to ask my system if it has that command cuz I cant do man CMD. How do you suggest I proceed? Btw, thnx for ur response :) – Charlie Parker Jun 15 '14 at 18:09
3

@CharlieParker The command is actually [ and is a synonym of test. But man [ or man test will give you the man page of the external command, whereas just about every shell out there has a built-in command with slightly different options, so you need to look this one up in your shell's manual. – Gilles 'SO- stop being evil' Jun 15 '14 at 18:33
If you want to test this simply on the command line, execute this command: if [ fileA -ef fileB]; then echo Yes; else echo No; fi – palswim May 09 '17 at 18:53

score 5 · Answer 2 · answered Nov 08 '11 at 12:04

5

function is-hardlinked() {
    r=yes
    [ "`stat -c '%i' $1`" != "`stat -c '%i' $2`" ] && r=no
    echo $r
}

answered Nov 08 '11 at 12:04

x-way

177

9

Note that this can be a false positive if the two files are on different filesystems but happen to have the same inode. You need to test the device number as well (stat -c %d). And if you're on Linux (given your stat command), your shell has the [ fileA -ef fileB ] to do all this directly. Also, your command gratuitously breaks with file names containing whitespace or \[?*, or begins with -: always put double quotes around command susbtitutions ("$(stat -c %i -- "$1")"). – Gilles 'SO- stop being evil' Jan 29 '13 at 15:41
3

Why would you use a bunch of cumbersome but portable constructs, and then the abjectly non-portable function keyword with a function name that (on account of containing a dash) violates POSIX conventions on allowed names? – Charles Duffy May 19 '17 at 22:25
You forgot to quote your $1 and $2. You might also want to use the $() syntax instead of backticks because the brackets make it clear where the command begins and where it ends and nesting is simpler. – josch Dec 30 '18 at 16:08
@Gilles'SO-stopbeingevil', ['s -ef checks whether the files are the same after symlink resolution, while GNU stat by default gets information from the symlink itself, so it's not equivalent. You can't use ['s -ef to check that two symlink files are hard linked to each other. GNU find's -samefile can be used instead or approaches based on various implementations of stat (provided you get both device and inode number as you said). – Stéphane Chazelas Jun 01 '22 at 11:12

score 3 · Answer 3 · answered Nov 07 '11 at 23:36

3

As the first poster suggest, you can write a script based on something like this on Linux:

stat -c '%i' fileA fileB fileC

answered Nov 07 '11 at 23:36

Not Now

2,572

7

This isn't enough: you'll get the same number for the two files if are on different filesystems but happen to have the same inode. You need to test the device number as well (stat -c %d). And if you're on Linux (given your stat command), your shell has the [ fileA -ef fileB ] to do all this directly. – Gilles 'SO- stop being evil' Jan 29 '13 at 15:42
@Gilles'SO-stopbeingevil', ['s -ef checks whether the files are the same after symlink resolution, while GNU stat by default gets information from the symlink itself, so it's not equivalent. You can't use ['s -ef to check that two symlink files are hard linked to each other. GNU find's -samefile can be used instead or approaches based on various implementations of stat (provided you get both device and inode number as you said). – Stéphane Chazelas Jun 01 '22 at 11:11

score 3 · Answer 4 · edited Jun 01 '22 at 10:20

3

With GNU find(1) version 4.2.11 or newer you can also use this:

if [ yes = "$(find fileA -prune -samefile fileB -printf yes)" ]; then
    echo yes
else
    echo no
fi

If fileA is the same file as fileB then find will print "yes" and the condition becomes true.

In contrast to using the file equality operator -ef this will spawn a new process.

edited Jun 01 '22 at 10:20

Stéphane Chazelas

544,893

answered Dec 30 '18 at 16:29

josch

355

score -3 · Answer 5 · answered Jan 09 '21 at 22:46

-3

You can do this very simply with the built-in bash operator -ef:

[[ file1 -ef file2 ]] && echo Same

If the condition evaluates to true (file1 and file2 are the same), then it prints "Same". Otherwise, nothing is output.

answered Jan 09 '21 at 22:46

Bill

95
1

1

This test will also be true if file1 is a symbolic link to file2, or the other way around. I don't really see a difference between this and the accepted answer (which has the same issue). – Kusalananda Jan 09 '21 at 23:13
@kusalananda Nope, docs specifically say it compares inode numbers: https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html – Bill Jan 09 '21 at 23:16
1

Sure, but it resolves symbolic links first. I suggest you test it. – Kusalananda Jan 10 '21 at 05:32

score -4 · Answer 6 · answered Jun 01 '22 at 10:11

-4

theres is other solution in the sh shell :

#!/bin/sh
file1='readlink $1'
file2='readlink $2'
if [ file1==file2 -o file2==file1 ]
then
echo "the files are linked with strong link"
else
echo "the files are not linked"
fi

the readlink give us the right to copy the inode into a string variable and compare it with other string variable . (two files have a string link have the same inode).

answered Jun 01 '22 at 10:11

Achraf Khabar

1

1

Consider updating your answer with code that is actually working. Note that your code will never call readlink, will not expand $1 nor $2, and will treat file1==file2 as one string, and file2==file1 as another, and both are always true (as they are non-empty strings). Additionally, readlink deals with symbolic links, not hard links. – Kusalananda Jun 01 '22 at 11:13

Are two files hardlinked?

6 Answers6