mjhjmtu

Look at the following:

$ echo ..aliases
..
$ echo ..foo
..
$ echo ..
..
$ echo ..xyz
..
$ echo .xyz.xyz
.xyz.xyz
$ echo .xyz.
.xyz.

Apparently this seems to be globbing something, but I don’t understand how the result comes together. From my understanding is an empty character class. It would be intuitive if

• it matched only the empty string; in this case, I’d expect bash to reproduce in its entirety since nothing matches it in this directory, but also match things like ..aliases (in the first example),


• or nothing at all; in this case, I’d expect bash to reproduce the string in total, too.

This is with GNU bash, version 4.4.23(1)-release.

The [ starts a set. A set is terminated by ]. But there is a way to have ] as part of the set, and that is to specify the ] as the first character. As an empty set doesn't make any sense, this is not ambiguous.

So your examples are basically all a dot followed by a set that contains a dot, therefore it matches two dots.

The later examples don't find any files and are therefore returned verbatim.

Only quoted strings are not subject to globbing:

$ echo "..aliases"
..aliases

But un-quoted strings are subject to globbing. An unquoted string that contains an * or a ? or (valid) (bracket expression) will be modified by the list of files that match it. In the same way as a * will transform into all the files in the matching directory and a ? will match files of only one character, a (valid) will match files with the characters inside the brackets. A dot is a valid character:

$ echo a[.]b
a[.]b

$ touch "a.b"
$ echo a[.]b
a.b

To be able to match a ] it should be the first character inside the brackets:

$ touch "a]b"
$ ls a]b
a]b

An empty bracket expression makes no sense (and is not expanded):

$ touch ab
$ ls ab
ls: cannot access 'ab': No such file or directory

That is why this works:

$ touch a]c abc afc azc a:c a?c aoc 
$ ls abfz:?]c
abc a:c a?c a]c afc azc

For [ the idea is similar:

$ touch a[c
$ ls a[c
a[c

but it could be at any position in a bracket expression:

$ ls abf[z:?]c
abc a:c a?c a[c a]c afc azc

$ ls abfz:?c
abc a:c a?c a[c a]c afc azc

The string you posted ..foo will match a dot followed by either a ], a ., a f, a o or a [. It is similar to:

$ echo a.fooc
a[c a]c afc aoc

And it will match as follows:

$ touch .] .f .o .[ .a .b .z

$ echo ..foo
.. .[ .] .f .o

Note that the directory entry .. does not need to be created as it exists inside every directory by default. But a simple dot . won’t be matched by a glob as it needs to be matched explicitly (by actually using a dot).

But that will not match ..aliases as the bracket expression will only match one character. To match several characters you need to use a * (anything):

$ touch ..a ..l ..i ..aliases ..alias ..ali
$ echo ..aliases
.. .[ .] .a

$ echo ..aliases*
.. .[ .] .a ..a ..ali ..alias ..aliases ..i ..l