Friday, 19 October 2007 09:51
Controlling Processes
Shell scripts were designed to run commands. Up to this point, all the scripts in the book have launched various commands, but all in isolation. The most you’ve seen so far is piping commands to connect the output of one command to the input of another. But the commands run from the scripts do not provide data back to the scripts, other than through writing data to a file. To make processes better fit into shell scripts, you need the capability to start and stop processes, as well as capture the output of processes into shell variables.
Friday, 19 October 2007 09:50
Controlling How Scripts Run
Once you get beyond some trivial scripts, you’ll soon find that a script that just runs command after command after command doesn’t work for most real-world scripts. Instead, you need the capability to perform some sort of logic within the program, test conditions, and take alternative measures if certain tests fail. You may need to perform some operation on each file in a directory or back up only selected files. Shell scripting languages offer a variety of ways to test values and then execute different commands based on the results of the tests. All of these things fall under the concept of controlling how your scripts run.
