Linux › Section K · Shell scripts › Topic K.2

Special variables and exit codes

A script becomes a real tool when it can take arguments and report whether it worked. The shell's special variables deliver the arguments, and exit codes carry success or failure back to whoever ran the script, which is also the key to finding out why a script went wrong.

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In this topic

Variables the shell fills in for you
Positional parameters and shift
Count, name and process ID
All the arguments: "$@" and "$*"
Exit codes and $?
When non-zero is not an error
Worked example: refusing bad arguments
Worked example: tracing with set -x
set -e, set -u and pipefail
ShellCheck
Common mistakes to avoid
Key takeaways

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