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Bash not equal string comparison

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# 1  
Old 10-09-2014
Bash not equal string comparison
Why does this cause an infinite loop?

Code:
#!/bin/bash


while [[ "$(ipcs | awk '{print $2}')" != "Semaphore" ]]; do
    echo "$(ipcs | awk '{print $2}')"

done
       
echo 
exit 0

I have verified I eventually get Semaphore so it should break out of the while loop.

Code:
$ echo $(ipcs | awk '{print $2}')
Shared shmid 262145 294914 2326531 Semaphore semid Message msqid

# 2  
Old 10-09-2014
Quote:
Originally Posted by cokedude
Why does this cause an infinite loop?

Code:
#!/bin/bash
 
 
while [[ "$(ipcs | awk '{print $2}')" != "Semaphore" ]]; do
    echo "$(ipcs | awk '{print $2}')"
 
done
 
echo 
exit 0

I have verified I eventually get Semaphore so it should break out of the while loop.

Code:
$ echo $(ipcs | awk '{print $2}')
Shared shmid 262145 294914 2326531 Semaphore semid Message msqid

Hi cokedude,
Could you please try following.

Code:
while [[ "$(ipcs | awk '{print $2}')" !~ "Semaphore" ]]; do
    echo "$(ipcs | awk '{print $2}')" 
done 
echo 
exit 0

Thanks,
R. Singh
# 3  
Old 10-09-2014
Quote:
Originally Posted by RavinderSingh13
Hi cokedude,
Could you please try following.

Code:
while [[ "$(ipcs | awk '{print $2}')" !~ "Semaphore" ]]; do
    echo "$(ipcs | awk '{print $2}')" 
done 
echo 
exit 0

Thanks,
R. Singh
For me what he tried looks right, but unfortunately he is comparing contents are not equal to a fixed string, so caught inside infinite loop.

---------- Post updated at 09:06 PM ---------- Previous update was at 09:04 PM ----------

Something like this should work I guess

Code:
#!/bin/bash


while [[ "$(ipcs | awk '{print $2}')" != *"Semaphore"* ]]; do
    echo "$(ipcs | awk '{print $2}')"

done
       
echo 
exit 0

I am bit confused with the contents

Quote:
Originally Posted by cokedude
Why does this cause an infinite loop?

Code:
#!/bin/bash


while [[ "$(ipcs | awk '{print $2}')" != "Semaphore" ]]; do
    echo "$(ipcs | awk '{print $2}')"

done
       
echo 
exit 0

I have verified I eventually get Semaphore so it should break out of the while loop.

Code:
$ echo $(ipcs | awk '{print $2}')
Shared shmid 262145 294914 2326531 Semaphore semid Message msqid

I tested like this, as soon as count reaches 500 it creates file and breaks while loop

Code:
#!/bin/bash

i=0
while [[ "$( ls )" != *"akshay"* ]]; do
	echo $i
	[ $i -eq 500 ] && touch unix.com_akshay_unix.com
i=$((i+1))
done

echo "released"

Last edited by Akshay Hegde; 10-09-2014 at 12:06 PM.. Reason: -- confused with the contents shown, after using awk '{ print $2 }'--
# 4  
Old 10-09-2014
No need to use awk:-
Code:
#!/bin/bash

ipcs | while read v1 v2 skip
do
        [ "$v2" != "Semaphore" ] && echo "$v2" || break;
done

exit 0

# 5  
Old 10-09-2014
Quote:
Originally Posted by RavinderSingh13
Hi cokedude,
Could you please try following.

Code:
while [[ "$(ipcs | awk '{print $2}')" !~ "Semaphore" ]]; do
    echo "$(ipcs | awk '{print $2}')" 
done 
echo 
exit 0

Thanks,
R. Singh
This won't work Smilie.

Code:
$ bash ./whilee1
./whilee1: line 2: conditional binary operator expected
./whilee1: line 2: syntax error near `!~'
./whilee1: line 2: `while [[ "$(ipcs | awk '{print $2}')" !~ "Semaphore" ]]; do'

Quote:
Originally Posted by Akshay Hegde
For me what he tried looks right, but unfortunately he is comparing contents are not equal to a fixed string, so caught inside infinite loop.

---------- Post updated at 09:06 PM ---------- Previous update was at 09:04 PM ----------

Something like this should work I guess

Code:
#!/bin/bash


while [[ "$(ipcs | awk '{print $2}')" != *"Semaphore"* ]]; do
    echo "$(ipcs | awk '{print $2}')"

done
       
echo 
exit 0

I am bit confused with the contents



I tested like this, as soon as count reaches 500 it creates file and breaks while loop

Code:
#!/bin/bash

i=0
while [[ "$( ls )" != *"akshay"* ]]; do
    echo $i
    [ $i -eq 500 ] && touch unix.com_akshay_unix.com
i=$((i+1))
done

echo "released"

Is there a trick to get this to work?

Code:
$ while [[ "$(ipcs | awk '{print $2}')" != *"Semaphore"* ]]; do
>     echo "$(ipcs | awk '{print $2}')"
> 
> done


$ bash ./whilee1

# 6  
Old 10-09-2014
The "trick" is to find out what the string is, not just what it looks like, so you can make a comparison which actually works.

I don't suppose you tried the while loop yet? It would be easiest to use that to check with, you could just print the value.

Code:
#!/bin/bash

ipcs | while read v1 v2 skip
do
        printf "Got [%s]\n" "$v2"

        [ "$v2" != "Semaphore" ] && echo "$v2" || break;
done

exit 0

# 7  
Old 10-09-2014
Bumping up posts or double posting is not permitted in these forums.

Please read the rules, which you agreed to when you registered, if you have not already done so.

You may receive an infraction for this. If so, don't worry, just try to follow the rules more carefully. The infraction will expire in the near future

Thank You.

The UNIX and Linux Forums.

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