Bash: double equals vs -eq

== is a bash-specific alias for =, which performs a string (lexical) comparison instead of the -eq numeric comparison. (It's backwards from Perl: the word-style operators are numeric, the symbolic ones lexical.)

To elaborate on bollovan's answer...

There is no >= or <= comparison operator for strings. But you could use them with the ((...)) arithmetic command to compare integers.

You can also use the other string comparison operators (==, !=, <, >, but not =) to compare integers if you use them inside ((...)).

Examples

• Both [[ 01 -eq 1 ]] and (( 01 == 1 )) do integer comparisons. Both are true.
• Both [[ 01 == 1 ]] and [ 01 = 1 ] do string comparisons. Both are false.
• Both (( 01 -eq 1 )) and (( 01 = 1 )) will return an error.

Note: The double bracket syntax [[...]] and the double parentheses syntax ((...)) are not supported by all shells.

If you want to do integer comparison you will better use (( )), where you can also use >= etc.

Example:

if (( $UID == 0 )); then
   echo "You are root"
else
   echo "You are not root"
fi