Shell Programming:COMMAND-LINE ARGUMENTS

COMMAND-LINE ARGUMENTS:

* In general, shell programs operate in a "batch" mode, that is, without interaction from the user, and so most of their parameters are obtained on the command line. Each argument on the command line can be seen inside the shell program as a shell variable of the form "$1", "$2", "$3", and so on, with "$1" corresponding to the first argument, "$2" the second, "$3" the third, and so on.

There is also a "special" argument variable, "$0", that gives the name of the shell program itself. Other special variables include "$#", which gives the number of arguments supplied, and "$*", which gives a string with all the arguments supplied.

Since the argument variables are in the range "$1" to "$9", so what happens there's more than 9 arguments? No problem, the "shift" command can be used to move the arguments down through the argument list. That is, when "shift" is executed, then the second argument becomes "$1", the third argument becomes "$2", and so on; and if a "shift" is performed again, the third argument becomes "$1"; and so on. A count can be specified to cause a multiple shift:

   shift 3

-- shifts the arguments three times, so that the fourth argument ends up in "$1".