Test

The test command (or [[ ]]) is used to test various conditions, or to compare strings.

When comparing strings in Bash you can use the following operators:

string1 = string2 and string1 == string2 - The equality operator returns true if the operands are equal.

- Use the = operator with the test [ command.
- Use the == operator with the [[ command for pattern matching.

   string1 != string2 - The inequality operator returns true if the operands are not equal.
   string1 =~ regex- The regex operator returns true if the left operand matches the extended regular expression on the right.
   string1 > string2 - The greater than operator returns true if the left operand is greater than the right sorted by lexicographical (alphabetical) order.
   string1 < string2 - The less than operator returns true if the right operand is greater than the right sorted by lexicographical (alphabetical) order.
   -z string - True if the string length is zero.
   -n string - True if the string length is non-zero.

Following are a few points to be noted when comparing strings:

   A blank space must be used between the binary operator and the operands.
   Always use double quotes around the variable names to avoid any word splitting or globbing issues.