Error handling in Bash

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Error handling in Bash

Author：JIYIK Last Updated：2025/03/21 Views：

This article introduces error handling in bash. Remember, understanding exit codes, options such as errexit and trap allow us to build robust scripts and manage bash problems more effectively.

Exit Codes in Bash

Handling errors based on exit codes is a standard technique for detecting command failures. This is especially true for external commands.

The curl command in bash is a good example of handling problems based on known error codes. In contrast to user-defined routines, external command error codes are fully documented.

${?}Stores the exit status of the last command executed before the given line. Code 0 means the command was executed successfully. Otherwise, something went wrong.

case {?} in
0) {
true # ok
} ;;
*) {
false # something went wrong
}

Bash error handling can be performed using simple exit codes. You can try until you find a lazier solution. At least, anyone would do so after performing some conditional handling of the problem based on the error code.

Error exit

Exiting on error is undoubtedly the most useful error detection and handling capability that bash programmers lack in the first place.

Trap, Exit, and Error

trap allows us to specify a command to be executed when the shell receives a signal. SIGNAL SPEC is the name of the signal. Some common signals are EXIT, ERROR, , DEBUGand RETURN.

We can use the trap -l command to list more signals. We can also use trap -p SIGSPEC to determine which commands are associated with a certain signal.

For example, we might want to determine which commands correspond to the ERR signal. In that case, we could type the following command line:

trap -p ERR

If the output is empty, trap has not yet associated any command with the signal.

_() { echo oops ; }
 trap _ ERR EXIT

Print signal commands now do not produce empty results.

enter:

trap -p EXIT ERR

Output:

trap -- '_' EXIT
trap -- '_' ERR

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