du :: Command Line

Hard Links and Shell Expansion

$ printf %s\\n {/usr,}/bin/{[,test}
/usr/bin/[
/usr/bin/test
/bin/[
/bin/test

Why isn’t the following command line expanding to the four arguments as above?

$ du -b {/usr,}/bin/{[,test}
55264	/usr/bin/[
51168	/usr/bin/test

It is expanding to four arguments. Hard link are into play here. It so happens that it is how du works by default for hard links.

Let’s use ls -i to inspect inode numbers:

$ \ls -lhi {/usr,}/bin/{[,test}
2634460 -rwxr-xr-x 1 root root 54K Nov  1 09:44 '/bin/['
2634545 -rwxr-xr-x 1 root root 50K Nov  1 09:44  /bin/test
2634460 -rwxr-xr-x 1 root root 54K Nov  1 09:44 '/usr/bin/['
2634545 -rwxr-xr-x 1 root root 50K Nov  1 09:44  /usr/bin/test

Note /bin/[ and /usr/bin/[ share the same inode number, as do /bin/test and /usr/bin/test.

But we can provide -l (short for --count-links), which is known to be available at least on GNU du:

$ du -lb {/usr,}/bin/{[,test}
55264	/usr/bin/[
51168	/usr/bin/test
55264	/bin/[
51168	/bin/test