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Full Discussion: Getting the iteration count in WHILE LOOP
Top Forums Shell Programming and Scripting Getting the iteration count in WHILE LOOP Post 302930654 by John K on Tuesday 6th of January 2015 07:56:14 AM
Old 01-06-2015
Getting the iteration count in WHILE LOOP
bash in RHEL 6.4

I have a requirement in which I want to get the iteration count from a WHILE LOOP.

The below mentioned simple script test.sh works fine. In the below script, the WHILE loop will iterate every 5 seconds infinitely until it greps the string BASKETBALL from /tmp/somestring.txt file. Once it greps the string BASKETBALL, it prints the string in the echo command and the loop is terminated using the break command.

Code:
# cat test.sh
export counter=1
while true
do
        if grep -iq BASKETBALL /tmp/somestring.txt
        then
        echo "This loop iterated $counter times before exiting.."
        break
        fi
        sleep 5
        counter=`expr $counter + 1`
done
#
# echo GOLF > /tmp/somestring.txt
# Now, execute the script and it will loop indefinitely as /tmp/somestring.txt file has the string GOLF 
# ./test.sh &
[1] 43208


# #### after few seconds populate /tmp/somestring.txt with the string basketball and the loop will stop iterating

# echo basketball > /tmp/somestring.txt
# This loop iterated 14 times before exiting..

[1]+  Done                    ./test.sh
#

The above script works fine. But, in my real-life script, there is a minor problem. The script itself is executed by root user and then the above portion of the script is executed by another user called appuser after a switch using su command. So, the script will look like below. The double quotes in red mark the beginning and end of commands to be executed by appuser. For this reason, I had to escape the double quotes used in the echo command.

Code:
# cat realLife.sh
sudo su - appuser -c "
export counter=1
while true
do
        if grep -iq BASKETBALL /tmp/somestring.txt
        then
        echo \"This loop iterated \$counter times before exiting..\"
        break
        fi
        sleep 5
        counter=`expr $counter + 1`
done
"
#

Although the WHILE LOOP runs fine with the above script, the echo command is always printing "This loop iterated 1 times before exiting.."
even if the loop iterated multiple times.



Demo:

Code:
# echo POLO > /tmp/somestring.txt
# Now, execute the script as root
# ./realLife.sh &
[1] 53717
# #### after few seconds populate /tmp/somestring.txt with the string basketball and the loop will stop iterating

# echo basketball > /tmp/somestring.txt
# This loop iterated 1 times before exiting..

[1]+  Done                    ./realLife.sh
#

I guess the double qutotes for the su command is confusing the shell. I wish there was some special variable which provides the loop count. Is there a workaround to fix this issue with realLife.sh script?
 

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LEARN ABOUT DEBIAN

ns_while

ns_lctl(3aolserver)					    AOLserver Built-In Commands 				       ns_lctl(3aolserver)

__________________________________________________________________________________________________________________________________________________

NAME

       ns_for, ns_foreach, ns_while, ns_lctl - Replacements for standard Tcl loop commands which enable monitoring and control

SYNOPSIS

       ns_for start test next body
       ns_foreach varname list body
       ns_foreach varlist1 list1 ?varlist2 list2 ...? body
       ns_while test body
       ns_lctl cancel id
       ns_lctl eval id script
       ns_lctl info id
       ns_lctl install command
       ns_lctl list
       ns_lctl pause id
       ns_lctl result id
_________________________________________________________________

DESCRIPTION

       The  ns_for, ns_foreach, and ns_while commands are replacements for cooresponding Tcl commands with the additional capability of monitoring
       and control through the ns_lctl command.

       ns_for start test next body
	      See the for(n) man page for usage.

       ns_foreach start test next body
	      See the foreach(n) man page for usage.

       ns_foreach varlist1 list1 ?varlist2 list2 ...? body
	      See the foreach(n) man page for usage.

       ns_while test body
	      See the while(n) man page for usage.

       ns_lctl cancel id
	      Mark the given loop to cancel at the next iteration, resulting in the loop returning with TCL_ERROR.

       ns_lctl eval id script

       ns_lctl info id

       ns_lctl install command

       ns_lctl list

       ns_lctl pause id

       ns_lctl result id

SEE ALSO

       for(n), foreach(n), while(n)

KEYWORDS

       threads, iteration, list, looping, cancel

AOLserver								4.5						       ns_lctl(3aolserver)
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