How does testing if a string is 'greater' than another work in Bash?

bash numeric-conversion
helpermethod picture helpermethod · Aug 16, 2012 · Viewed 34.3k times · Source

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

Michał Górny picture Michał Górny · Aug 16, 2012

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.

Related questions

How to concatenate string variables in Bash

In PHP, strings are concatenated together as follows: $foo = "Hello"; $foo .= " World"; Here, $foo becomes "Hello World". How is this accomplished in Bash?

Read More
How can I check if a directory exists in a Bash shell script?

What command can be used to check if a directory exists or not, within a Bash shell script?

Read More
How do I tell if a regular file does not exist in Bash?

I've used the following script to see if a file exists: #!/bin/bash FILE=$1 if [ -f $FILE ]; then echo "File $FILE exists." else echo "File $FILE does not exist." fi What's the correct syntax to use if I only want …

Read More