3.3 Shell Functions

Shell functions are a way to group commands for later execution using a single name for the group. They are executed just like a "regular" command. When the name of a shell function is used as a simple command name, the list of commands associated with that function name is executed. Shell functions are executed in the current shell context; no new process is created to interpret them.

Functions are declared using this syntax:

[ function ] name () { command-list; }

This defines a shell function named name. The reserved word function is optional. If the function reserved word is supplied, the parentheses are optional. The body of the function is the command-list between { and }. This list is executed whenever name is specified as the name of a command. The exit status of a function is the exit status of the last command executed in the body.

Note that for historical reasons, the curly braces that surround the body of the function must be separated from the body by blanks or newlines. This is because the braces are reserved words and are only recognized as such when they are separated by whitespace. Also, the command-list must be terminated with a semicolon or a newline.

When a function is executed, the arguments to the function become the positional parameters during its execution (see section 3.4.1 Positional Parameters). The special parameter '#' that expands to the number of positional parameters is updated to reflect the change. Positional parameter 0 is unchanged. The FUNCNAME variable is set to the name of the function while the function is executing.

If the builtin command return is executed in a function, the function completes and execution resumes with the next command after the function call. When a function completes, the values of the positional parameters and the special parameter '#' are restored to the values they had prior to the function's execution. If a numeric argument is given to return, that is the function's return status; otherwise the function's return status is the exit status of the last command executed before the return.

Variables local to the function may be declared with the local builtin. These variables are visible only to the function and the commands it invokes.

Functions may be recursive. No limit is placed on the number of recursive calls.