Using the "true" Command (with examples)
The “true” command is a basic Unix command that does nothing and always returns a successful exit status code of 0. It is often used in shell scripts or command line executions to signify the success of a particular operation or to ensure that a command always exits with 0.
Use Case 1: Returning a successful exit code
Code:
true
Motivation:
The motivation for using the “true” command in this case is to explicitly return a successful exit code. This can be useful in scenarios where you need to indicate the success of a script or command, even if there are no specific actions or operations to be performed.
Explanation:
The “true” command is a simple shell command that does not perform any operations. When executed, it immediately exits with a status code of 0, indicating successful execution.
Example Output:
$
In this example, executing the “true” command does not produce any output. However, when checking the exit status using the “$?” variable, it will be set to 0, indicating success.
Use Case 2: Using the “true” command with the logical OR operator
Code:
command_1 || true
Motivation:
The motivation for using the “true” command in this case is to ensure that a command always exits with a successful status code. This is particularly useful when executing a command that may fail but should not impact the overall success of the script or command execution.
Explanation:
In this use case, the “true” command is combined with the logical OR operator “||”. The first command, “command_1”, is executed, and if it fails (returns a non-zero exit status code), the “true” command is executed. Since the “true” command always returns 0, the overall exit status of the combined command will be 0.
Example Output:
command_1 failed
In this example, let’s say “command_1” fails and returns an exit status code of 1. When executing the command sequence “command_1 || true”, the failed output of “command_1” is displayed, but the overall exit status of the command sequence will be 0, indicating success.
Use Case 3: Powering up the “true” command with the logical AND operator
Code:
command_1 && true
Motivation:
The motivation for using the “true” command in this case is to ensure that a command only continues execution if the previous command was successful. This is helpful when you want to execute subsequent commands, but only if the preceding commands executed without errors.
Explanation:
In this use case, the “true” command is combined with the logical AND operator “&&”. The first command, “command_1”, is executed, and if it succeeds (returns a successful exit status code of 0), the “true” command is executed. Since the “true” command always returns 0, the subsequent commands after “&&” will be executed.
Example Output:
command_1 succeeded
In this example, let’s say “command_1” succeeds and returns an exit status code of 0. When executing the command sequence “command_1 && true”, the success output of “command_1” is displayed, and the subsequent commands after “&&” will also be executed.
Conclusion
The “true” command is a simple yet powerful command that can be used in various scenarios. It allows for explicit success indication, ensures that a command always exits with a successful status code, and controls the execution of subsequent commands based on the success of the previous command. By understanding these different use cases, you can leverage the “true” command to enhance your shell scripts and command line executions.
