function::is_return - Linux


The is_return function in Linux evaluates whether the value of a variable or expression satisfies a given condition. It returns a boolean value, true if the condition is met, and false otherwise. This function is particularly useful for complex conditional checking and logical operations in scripts and programs.


is_return "expression"
  • expression: The condition or expression to evaluate. It can be a variable, a comparison, or any other valid expression that returns a boolean value.


This function does not accept any options or flags.


Simple Usage: Check if a file is readable:

is_return "[[ -r /path/to/file ]]"

Complex Condition: Check if a file size is less than 1 MB:

is_return "[[ -s /path/to/file ]] && [[ $(stat -c%s /path/to/file) -lt 1000000 ]] ..."

Common Issues

  • Syntax Error: Ensure that the expression is enclosed in double quotes and follows the correct syntax.
  • Invalid Expression: Make sure the expression returns a boolean value.
  • Unexpected Output: Verify that the condition being evaluated matches the intended logic.


  • Use with conditional statements (e.g., if, while) to control program flow based on the result of the evaluation.
  • Combine with other boolean evaluation functions, such as is_true and is_false, to create complex conditional chains.
  • Integrate into scripts or programs to handle complex logical checks and decision-making.

Related Commands

  • test
  • [[
  • condition
  • expr