Bash-Beginners-Guide

# Calculate the average of a series of numbers.
SCORE="0"
AVERAGE="0"
SUM="0"
NUM="0"
while true; do
echo -n "Enter your score [0-100%] ('q' for quit): "; read SCORE;
if (("$SCORE" < "0")) || (("$SCORE" > "100")); then
echo "Be serious. Common, try again: "
elif [ "$SCORE" == "q" ]; then
echo "Average rating: $AVERAGE%."
break
else
SUM=$[$SUM + $SCORE]
NUM=$[$NUM + 1]
AVERAGE=$[$SUM / $NUM]
fi
done
echo "Exiting."
Note how the variables in the last lines are left unquoted in order to do arithmetic.
9.3. The until loop
9.3.1. What is it?
The until loop is very similar to the while loop, except that the loop executes until the TEST-COMMAND
executes successfully. As long as this command fails, the loop continues. The syntax is the same as for the
while loop:
until TEST-COMMAND; do CONSEQUENT-COMMANDS; done
The return status is the exit status of the last command executed in the CONSEQUENT-COMMANDS list,
or zero if none was executed. TEST-COMMAND can, again, be any command that can exit with a success or
failure status, and CONSEQUENT-COMMANDS can be any UNIX command, script or shell construct.
As we already explained previously, the ";" may be replaced with one or more newlines wherever it appears.
9.3.2. Example
Bash Guide for Beginners
An improved picturesort.sh script (see Section 9.2.2.2), which tests for available disk space. If not
enough disk space is available, remove pictures from the previous months:
#!/bin/bash
# This script copies files from my homedirectory into the webserver directory.
# A new directory is created every hour.
# If the pics are taking up too much space, the oldest are removed.
while true; do
Chapter 9. Repetitive tasks 112