In Bash, are wildcard expansions guaranteed to be in order?

Solution 1:

Yes, globbing expansion is alphabetical.

From the Bash man page:

Pathname Expansion

After word splitting, unless the -f option has been set, bash scans each word for the characters *, ?, and [. If one of these characters appears, then the word is regarded as a pattern, and replaced with an alphabetically sorted list of file names matching the pattern.

Solution 2:

It is documented behavior for bash so you can depend upon it in your scripts. It also has been true of other Bourne compatible shells for a very long time ... though there may be corner cases regarding case folding or non-alphanumeric characters.

(The resulting list, in bash will be in almost "ASCII-betical" order --- except that lower and upper case letters will be collated together as if there were no case differences but with lower case collated before their upper case equivalents. All non-alphabetics should collate into the same order as they appear in ASCII).

As others have pointed out this could be perturbed by your language related environment settings: LANG generally and LC_COLLATE more specifically. In might be safest to run commands that depend on glob expansion ordering under an env command to clear the environment (using -i or -u as appropriate) or to pipe the results through sort to ensure robust sequencing.

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Solution 3:

While glob expansions are sorted alphabetically, they also obey the shell's langage setting.

Make sure to set this to "C" in your script if you intend this to be portable.