While loop never ends

Question

I'm working with bash and I'm trying to do something like this:

A=1
while [ $A=1 ]; do
    read line
    echo $line | grep test >/dev/null   
    A=$?
    echo $A
done 

This script never ends even when the grep finishes successfully and A is set to 0. What am I missing here? Below is a sample of the output.

$ ./test.sh

asdf

1

test

0

hm...

1

Answer 1

I find Bash's syntax pretty awful - have you tried something like:

while [ $A -eq 1 ] ... ?

It may be trying to re-assign 1 to $A or something strange like that.

Answer 2

Try:

while [ $A -eq 1 ]; do

Answer 3

Have you not tried this

while [ $A == "1" ]
   ....
done

Edit: Whoops since Dan mentioned my error I graciously admit my mistake and have edited this accordingly - Thanks Dan for the heads up...

while [ $A -eq 1 ]
   ....
done

Sorry! :( Hope this helps, Best regards, Tom.

Answer 4

You need to use the correct comparison operator. Bash has different operators for integer and string comparison.

In addition, you need the correct spacing in the comparison expression.

You need

while [ $A -eq 1 ]; do

See here for more

Answer 5

you can do this instead. No need to call external grep.

while true; do
    read line
    case "$line" in
      *test* ) break;;
    esac
done 
echo $line

Answer 6

All of your answers are in the Advanced Bash-Scripting guide. It is awesome.

Answer 7

So far all answers (except for ghostdog74's) have focused on the integer/string and spacing problem. While this is correct, I believe the code should be completely re-factored.

Let's say the idea is to process lines until one line matches a regex ('test' in this case). Using grep:

while read line; do      
  grep -q test <<< "$line" && break
  # do something with $line
done

or using double brackets:

while read line; do      
  [[ "$line" =~ test ]] && break
  # do something with $line
done

http://tldp.org/LDP/abs/html/x16608.html http://tldp.org/LDP/abs/html/testconstructs.html#DBLBRACKETS