Passing parameters to a dependend program

When you execute a program in many cases you have to hand over one or more parameters. They tell the program what to do. A good example are the archivers supported by Arcgsh: They take parameters that tell

• what to do (e. g. add files to an archive, extract from an archive) and

• on what files to operate (e. g. the archive, archive elements or files).

All these parameters are handed over to the dependend program as a string of charactersm, the so-called command line. However, there is a tight TOS limitation that restricts the total parameter string length to 125 characters. If you specified more characters on the command line they are gracelessly clipped off.

Of course there is a need to pass more than 125 characters to a program, e. g. when an archiver is called with a lot of files that should be processed. Consequently procedures have been worked out by several people to achieve this. These extended parameter passing schemes work as follows: The calling program communicates the long parameter string to the callee by use of an certain environment variable. The called program reads its environment and checks for the variable that indicates an extended parameter string. If it finds that variable it uses it. Otherwise it takes its parameter from the command line. It is clear that both caller and callee must support the extended parameter passing scheme.

The most common extended parameters passing schemes are the xArgv and the ARGV scheme. Arcgsh supports both these schemes and can therefore hand over more than 125 characters to a dependend program that also supports the xArgv or ARGV parameter passing scheme. The archivers arc and zoo are examples for such programs.

Arcgsh supports xArgv and ARGV for registered users only. On how to register see section (page )!