Bash While loop Not Ending

Question

I was playing with bash programming. I have written a simple bash program which takes input from reader. If reader typed the string "bye" the while loop ends. So the program is pretty simple I have written something like this

#!/bin/sh
inputString="hello"
while [ inputString != "bye" ]
do
    echo "Please write something (bye to quit)"
    read inputString
    echo "You typed : ${inputString}"
done

It works perfectly until user type two words at a time.

If user type something like this

bye bye

Program crashes giving the following error

./WhileLoop.sh: 5: [: bye: unexpected operator

How can i modify the code so that program can take multiple input?

Take a look at shellcheck.net

Cyrus
– Cyrus

2014-09-07 07:53:58 +00:00
Commented Sep 7, 2014 at 7:53 — Cyrus
– Cyrus, Commented Sep 7, 2014 at 7:53

Zulu · Accepted Answer · 2014-09-07 14:33:52Z

3

Put double quotes around inputString in while's condition. Without double quotes, if your variable is empty, it will raise a error.

Update:

There's a typo on script, add $ before inputString, make variable substitution: while [ "$inputString" != "bye" ]

edited Sep 7, 2014 at 14:33

answered Sep 7, 2014 at 7:42

Zulu

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3 Comments

mirmdasif Over a year ago

That's the correct answer. All I need is to put $inputString into double quotes

clt60 Over a year ago

@sadasidha No, this ISN'T the correct answer. The quoted "inputString" isn't the same as the quoted "$inputString". So, yes, need to quote, but need to put the $ in the front. Please, MARK only really correct answers.

chepner Over a year ago

@jm666 I assume the lack of a $ is a typo in the question, because the posted code would not produce the given error. (It would simply loop forever because the two literal strings would never equal each other.)

clt60 · Accepted Answer · 2014-09-07 14:15:23Z

2

In bash 4+ you can also:

while read -r -p 'Please write something (bye to quit)>' ans
do
   echo "your answer =$ans="
   #convert the $ans to lowercase to match "BYE"
   #use matching to match "bye bye" or "byeanythinghere"
   #in case of double [[ don't needed the "", but never harm, so using it
   [[ "${ans,,}" =~ bye.* ]] && exit 0
   #[[ ${ans,,} =~ bye.* ]] && exit 0   #works too
   echo "not bye - yet"
done

edited Sep 7, 2014 at 14:15

answered Sep 7, 2014 at 12:52

clt60

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3 Comments

chepner Over a year ago

FYI, the ,, operator requires bash 4.

clt60 Over a year ago

@chepner never remember what knows old and new... i have 4.3 ;) edited.

chepner Over a year ago

It helps when Mac OS X stays stuck on 3.2 :)

Austin Phillips · Accepted Answer · 2014-09-07 07:25:35Z

1

Use a $ in front of a variable to have it expanded. $inputString

answered Sep 7, 2014 at 7:25

Austin Phillips

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1 Comment

mirmdasif Over a year ago

No it's not working the problem still exist if I write while loop like this while [ $inputString != "bye" ]

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