Question

In Bash I can write the following test

[[ "f" > "a" ]]

which results in returning 0, i.e. true. How does bash actually perform this string comparison? From my understanding > does an integer comparison. Does it try to compare the ASCII value of the operands?

Answer 1

From help test:

  STRING1 > STRING2
                 True if STRING1 sorts after STRING2 lexicographically.

Internally, bash either uses strcoll() or strcmp() for that:

else if ((op[0] == '>' || op[0] == '<') && op[1] == '\0')
  {
    if (shell_compatibility_level > 40 && flags & TEST_LOCALE)
      return ((op[0] == '>') ? (strcoll (arg1, arg2) > 0) : (strcoll (arg1, arg2) < 0));
    else
      return ((op[0] == '>') ? (strcmp (arg1, arg2) > 0) : (strcmp (arg1, arg2) < 0));
  }

The latter actually compares ASCII codes, the former (used when locale is enabled) performs a more specific comparison which is suitable for sorting in given locale.