"Subject not capitalized" error on some environments when subject is capitalized

[laurivan]

Description

On some systems the subject of a commit message is erroneously reported as not being capitalized.

$ git commit -m "Version update"
ERROR: commit message not properly formatted
- line 1: subject not capitalized
  Version update

Continue anyway? [yes/no/edit] no

Cause

I don't know which systems or environments are affected but it seems that the problem is matching the subject line with a regular expression that uses a "traditional" character range:

[[ ${subject} =~ ^[a-z] ]]

This "usually" works but is dependent on at least the user's locale, especially the LC_COLLATE environment variable which can change what [a-z] means. On some systems it might mean [aAbBcC...] instead of the expected [abcd...] which makes it match uppercase letters as well.

Fix

The fix is as simple as replacing [a-z] in the regex with [[:lower:]] which is always interpreted as [abc...xyz]