🧾 Commands and Exit Codes

Every command returns an exit code that indicates success or failure. Understanding these codes is critical for scripting robust workflows.

🔢 Exit Code Meaning

Exit codes range from 0 to 255. By convention: - 0 = Success - 1–255 = Various types of failures

Check last command’s exit code with $?:

$ ls /nonexistent
ls: cannot access '/nonexistent': No such file or directory
$ echo $?
2

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🧪 Testing Exit Codes in Scripts

Use conditional statements to check results:

#!/bin/sh
command_that_might_fail
if [ $? -eq 0 ]; then
    echo "Success!"
else
    echo "Something went wrong."
fi

Or more concisely:

if command_that_might_fail; then
    echo "Success!"
else
    echo "Failure occurred."
fi

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🧰 Common Exit Codes

Code	Meaning	Examples
0	Success	Normal completion
1	General error	Misuse of shell builtins
2	Misuse of shell builtin	Incorrect usage
126	Command found but not executable	Permission denied
127	Command not found	Typo or missing PATH entry
130	Script terminated by Ctrl+C	Signal SIGINT received

Full list available in sysexits.h or man sysexits.

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🧪 Practical Example

Here’s how to handle errors gracefully:

#!/bin/sh

backup_file() {
    cp "$1" "$1.bak"
    return $?
}

backup_file important.conf
if [ $? -ne 0 ]; then
    echo "Backup failed!" >&2
    exit 1
fi
echo "Backup completed."

This ensures failures don't get ignored silently.

👉 Continue to: Path and Executables