Practical UNIX

Executing Code Based on Test Results

All programming languages have some way of deciding whether to execute code based on whether a condition is true or not. The shell provides this to you as the if statement. A small if statement has the general syntax shown on the right, next to a code example on the left:

if [ "$CNT" -eq 25 ]            #    if condition
then                            #    then
    cp acme /tmp/archive        #       command(s)
    rm /tmp/acme                #
fi                              #    fi

The full possible general syntax of the if statement is shown on the left, with example code on the right:

if [ "$CNT" -eq 25 ] # if condition 1 then # then cp acme /tmp/archive # command(s) rm /tmp/acme # elif [ "$CNT" -gt 25 ] # elif condition 2 then # then cp acme2 /tmp/archive # command(s) elif [ "$CNT" -gt 0 ] # elif condition 3 then ...