Similar to the for
command, while
is also the command for loop operations. The command next to while
is evaluated. If it is successful or 0 then the commands inside do
and done
are executed.
The purpose of a loop is to test a certain condition or expression and execute a given command while
the condition is true (while
loop) or until
the condition becomes true (until
loop):
while condition do commands done |
until condition do commands done |
The following is the while_01.sh
script, in which we read a file and display its it's content:
#!/bin/bash file=/etc/resolv.conf while IFS= read -r line # IFS : inter field separator do # echo line is stored in $line echo $line done < "$file"
Let's test the program:
$ chmod +x while_01.sh $ ./while_01.sh
The following will be the output after executing the preceding commands:
nameserver 192.168.168.2 search localdomain
In the following script while_02.sh
, we are printing number 1–10 on the screen using the while...