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Shell Variable visibility

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# 8  
Old 01-14-2017
In the cat ... | while read you should see another pid while doing ps -ef | grep <your script pid>.
Another pid will be subshell pid with your script PID as parent.

For instance :

Code:
echo $$
var=0
echo "junk" | while read line
do
	sleep 100
	((var++))
done
echo $var

Yields :
Code:
user@machine:~/posao$ ./sshell.sh 
2775

Code:
user@machine:~/work$ ps -ef | grep 2775
user     2775  2488  0 05:46 pts/0    00:00:00 bash
user     2777  2775  0 05:46 pts/0    00:00:00 bash # var will be incremented in shell with PID 2777, when it completes it will exit, parent (our script with PID 2775) will not be aware of var increment.
user     2782  2528  0 05:46 pts/1    00:00:00 grep 2775
user@machine:~/work$ ps -ef | grep sleep
user     2778  2777  0 05:46 pts/0    00:00:00 sleep 100
user     2784  2528  0 05:46 pts/1    00:00:00 grep sleep

Other example :

Code:
echo $$
var=0
while read line
do
	sleep 100
	((var++))
done < junk.txt
echo $var

Yields :

Code:
user@machine:~/work$ ./shell.sh 
2755

Code:
user@machine:~/work$ ps -ef | grep 2755
user     2755  2488  0 05:40 pts/0    00:00:00 bash
user     2756  2755  0 05:40 pts/0    00:00:00 sleep 100 # after this, var will be incremented in shell with pid 2755 (our script).
user     2759  2528  0 05:41 pts/1    00:00:00 grep 2755

Notice the difference in bash count with parent / children relation in both examples.

Hope that helps
Regards
Peasant.
This User Gave Thanks to Peasant For This Post:
dae
# 9  
Old 01-14-2017
Quote:
Originally Posted by dae
[..]
2. Scrutinizer, I applied your suggestion (illustration below with fnct_dae_V3) but, in that case, it seems that I can not keep the value of the variable with that syntax:

fnct_dae_V3:


Code:
[x004191a@xsnl11p317a log]$ fnct_dae_V3 ()
> {
>
>   echo "PID_Fonction: $$"
>
>   var=0
>
>   cat "STG_INSTNCE_COMPLTED_01_451_20170112193018.log" |
>
>   {
>
>     while read -r line
>     do
>
>       if [[ $(echo "$line" | grep -i 'completed') ]]
>       then
>
>         ((var++))
>
>       echo "- INSIDE WHILE:var:$var"
>       echo "PID_WHILE: $$"
>
>       fi
>
>     done
>
>   }
>
>   echo "- OUTSIDE WHILE:var:$var"
>
> }
[x004191a@xsnl11p317a log]$ fnct_dae_V3
PID_Fonction: 15468
- INSIDE WHILE:var:1
PID_WHILE: 15468
- INSIDE WHILE:var:2
PID_WHILE: 15468
- INSIDE WHILE:var:3
PID_WHILE: 15468
- INSIDE WHILE:var:4
PID_WHILE: 15468
- OUTSIDE WHILE:var:0
[x004191a@xsnl11p317a log]$

So, I allow myself to ask you one more time: how is it possible to lose the value of the variable if the whole execution use a unique PID (cf. fnct_dae_V1 and I assume fnct_dae_V3) ?

Thanks again, Smilie
As Don noted earlier, you did not apply my suggestion. Look carefully: the second brace is in the wrong place:

wrong:
Code:
    done
  }
  echo "- OUTSIDE WHILE:var:$var"
}

right:
Code:
    done
    echo "- OUTSIDE WHILE:var:$var"
  }
}

This User Gave Thanks to Scrutinizer For This Post:
dae
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