BASH Shell Infinite loop with IF ELSE Statment

Question

Ok I know I've asked a similar question, I understand how to do an infinate loop:

while [ 1 ]
do
    foo
    bar
        then
sleep 10
done

But if I want to run some (quite a few) IF ELSE Statements in this loop how would I get the script to carry on looping once they had completed how would I go about this?

you mean how you can do an if/else statement inside the while ? I dont understand — webbi
– webbi, Commented Nov 3, 2011 at 20:03
Yes thats it, I have have pretty big script with a fair few if else statements in it. What I want to do is loop the entire script. — bikerben
– bikerben, Commented Nov 3, 2011 at 20:08
@bikerben: Well, just wrap the shell code you want in a while/do/done. And if you intend to break out of it with Ctrl-C (or any other method of killing it), perhaps have a look at the trap command. — Jan Hudec
– Jan Hudec, Commented Nov 3, 2011 at 21:13

Jan Hudec · Accepted Answer · 2011-11-03 20:25:41Z

7

while :; do
    if cond1; then
        whatever
    elif cond2; then
        something else
    else
        break
    fi
done

You do infinite loop using while true or using true's shorter alias :. [ 1 ] is needlessly complicated and is not what you think it is ([ 0 ] is also true!). Remember, the condition in if and while is arbitrary command whose exit status (zero = true, nonzero = false) is used as the condition value and [ is just alias for special test command (both built-in in most shells, but they don't have to be).
Any shell construct is allowed between do/done including conditionals, more loops and cases.
Use break to terminate innermost loop from inside (just like most other languages).

edited Nov 3, 2011 at 20:25

answered Nov 3, 2011 at 20:13

Jan Hudec

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1 Comment

webbi Over a year ago

I bet he's not asking that... I don't understand why he says: "What I want to do is loop the entire script"

chown · Accepted Answer · 2011-11-03 20:11:47Z

0

An if in bash is just: if [ some test ]; then some_command; fi:

while [ 1 ]
do
    if [ some test ]
    then
        some command
    else
        other cmd
    fi
sleep 10
done

Bash Scripting Guide

answered Nov 3, 2011 at 20:11

chown

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1 Comment

Jan Hudec Over a year ago

No. if in shell is just if some test; then some command; fi. The [ is a command used for comparing values and checking existence of files, but there are many cases where you either need some arbitrary command (which, grep, ...) or where test is not enough and end up going with expr.

zero323 · Accepted Answer · 2013-11-01 01:07:06Z

0

Correction to chown case added brake to finish the loop Corrected

while [ 1 ]
do
    if [ some test ]
    then
        some command
    brake
    else
        other cmd
    fi
sleep 10
done

edited Nov 1, 2013 at 1:07

zero323

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answered Nov 1, 2013 at 0:45

mudrii

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