Editing Multics (section)

=== Active functions ===
The Multics [[shell (computing)|shell]] language supports "active functions", which are similar to commands, but which return a string value.  An active function is called by putting the active function name and the arguments to the active function in square brackets {{mono|[}} and {{mono|]}}. The string returned by the active function is substituted into the command in place of the call to the active function.  For example, when the command {{mono|echo [working_dir]}} is processed, the active function {{mono|working_dir}} is run; it returns the full path of the [[working directory]], which is substituted into the command, so that the {{mono|echo}} command prints the working directory.

Some programs can act either as commands or as active functions; when run as a command, its result is printed, and when run as an active function, its result is returned as a string.<ref name="multics-commands" />

Some common active functions are:

* {{mono|[[Floor and ceiling functions|ceil]]}} - returns the smallest integer greater than or equal to the argument
* {{mono|[[Floor and ceiling functions|floor]]}} - returns the largest integer less than or equal to the argument
* {{mono|home_dir}} ({{mono|hd}}) - returns the [[home directory]]
* {{mono|[[ltrim]]}}
* {{mono|[[rtrim]]}}
* {{mono|[[Truncation|trunc]]}} - returns the integer part of the argument
* {{mono|working_dir}} ({{mono|wd}}) - returns the [[working directory]]