### 7.1 Child Processes

Unlike some other implementations of SCCS, CSSC tools do not usually execute each other. This means for example that `delta` does not invoke `get` to extract the previous version of the file, and `prs` doesn’t use `get` when processing the `:GB:` keyword.

There are a small number of exceptions to this rule :-

`sccs`

  The `sccs` driver program can be used to invoke any of the other tools in the suite. See Known Problems, for a discussion of the issues this raises.

`delta`

  The `delta` program runs a program to validate the Modification Request Numbers offered by the user. See Modification Request Numbers.

`sccsdiff`

  The `sccsdiff` program is a shell script, and invokes `get`, `diff` and `pr`, as well as other tools such as `cat`, `test` and `rm`. The `sccsdiff` program must not be installed set-user-id.

The driver program `sccs` takes a number of precautionary steps if it detects that it is running set-user-id or set-group-id. These steps are described below, as part of the discussion of each environment variable.