Practical LPIC-1 Linux Certification Study Guide by David Clinton

Author:David Clinton
Language: eng
Format: epub
Publisher: Apress, Berkeley, CA

Loops

Many scripts require repeated actions while—or until—a certain condition is met. You might, for example, want a script to launch some process only after a preceding process has completed. You could write a script to test for the existence of the first process so that, when the test fails, the new process is started.

Like anything else related to scripting, there really is no end to the possible scenarios a fertile imagination can dream up. Unfortunately, to illustrate the principles, you’ll have to come back to my silly and unimaginative examples.

Here’s a loop that, using while, will continue as long as a variable called COUNTER—set to start at 10 and reduced one integer at a time—remains higher than 2. Try it for yourself:

#!/bin/bash

#example of while loop:

declare -i COUNTER

COUNTER=10

while [ $COUNTER -gt 2 ]; do

echo The counter is $COUNTER

COUNTER=COUNTER-1

done

exit 0

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