Usage message
In computer programming, a usage message or help message is a brief message displayed by a program that utilizes a command-line interface for execution. This message usually consists of the correct command line usage for the program and includes a list of the correct command-line arguments or options acceptable to said program.
Usage messages are utilized as a quick way for a program to inform the user of proper command syntax, and should not be substituted for proper error messages or for detailed documentation such as a man page.
Pattern
On Unix-like platforms, usage messages usually follow the same common pattern:- They often begin with "Usage:", the command, followed by a list of arguments.
- To indicate optional arguments, square brackets are commonly used, and can also be used to group parameters that must be specified together.
- To indicate required arguments, angled brackets are commonly used, following the same grouping conventions as square brackets.
- Exclusive parameters can be indicated by separating them with vertical bars within groups.
Examples
Here is an example based on the NetBSD :Usage: program req1 req2
- [options">opt1 [opt2
This would indicate that "program" should be called with:
- [options without operands:,,, . Note that in this case some parameters are case-sensitive
- exclusive options:,
- options with operands:
- exclusive options with operands:,
- required arguments:,
- optional argument, which may be used with or without
- optional argument, which requires
Implementation
To print a usage statement in a shell script, one might write:case "$arg" in
...
h) printf 'Usage: %s parameter1 parameter2...\n' "$"
exit 0
;;
...
esac