Does number of hardlinks to a directory correspond to the number of subdirectories in it?

Question

When displaying directories using ls -l, their number of links (the second field in the output) is at least two: one for the dir name and one for .

$ mkdir foo
$ ls -l
total 2
drwxr-xr-x  2 user   wheel  512  4 oct 14:02 foo

Is it safe to always assume that the number of links above 2 corresponds to the number of subdirectories in this dir (.. links) ?

why not use something like `ls -d1 */ | wc -l` That'll also take into account links, if thats what you want. — Sirex, Oct 04 '10 at 11:35

score 2 · Answer 1 · answered Oct 04 '10 at 11:34

2

You are correct to observe that all directories contain . and .., so if you subtract two from the output of

ls -la | grep '^d' | wc -l

you should get the number of directories in your current working directory.

answered Oct 04 '10 at 11:34

MadHatter

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natxo asenjo · Answer 2 · 2010-10-04T12:17:39.337

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this does not answer your question about ls -l, but I use tree -d for this, it works very nicely.

edited Oct 04 '10 at 12:17

answered Oct 04 '10 at 12:01

natxo asenjo

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score 1 · Accepted Answer · answered Oct 04 '10 at 11:39

1

While generally you can only use symbolic links to directories, which will not affect the link count, there are some circumstances where hard-links are possible for directories (IIRC OSX's TimeMachine feature uses such links) so it might not always be guaranteed.

You would be safer passing a scan using ls and grep (or perhaps find) to the wc command to count the number of sub-directories actually present rather than trying to guess from the current directories link count.

answered Oct 04 '10 at 11:39

David Spillett

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I don't understand - unless you use the -i flag to compare the results, ls won't find any duplicates. That being said, I've never encountered multiple hardlinks to directories (disregarding . and ..) and I'm highly surprised that some tool should use them by design. I wouldn't be surprised if standard tools such as find, ls -R and tar assume this property to hold. – reinierpost Oct 12 '10 at 08:20

score 0 · Answer 4 · answered Oct 04 '10 at 11:50

0

I would use find

find ./foo -type d | wc -l

eventually with the -maxdepth option

answered Oct 04 '10 at 11:50

marcoc

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Does number of hardlinks to a directory correspond to the number of subdirectories in it?

4 Answers4