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# 1  
Old 07-04-2013
Hammer & Screwdriver Process count problem in script
Hi,

I am trying to make a script which should execute if the same is not getting executed already.
To implement this check, I wrote a fragment of code as below

Code:
$ cat abc.sh
#!/bin/bash

check=0

#grepping "sh -x abc.sh" because if i check only for "abc.sh" and the file is open in say vim, it would increase the count unnecessarily 
check=`ps -ef|grep "sh -x abc.sh"|grep -v grep|wc -l`

echo "$check"

sleep 180

On execution the output is as below [using -x for verbose purpose]
Code:
$ sh -x abc.sh
+ check=0
++ ps -ef
++ grep 'sh -x abc.sh'
++ grep -v grep
++ wc -l
+ check=2
+ echo 2
2
+ sleep 180

However during this sleep time if I am checking the process count from another terminal it gives me check=1

Code:
$ check=`ps -ef | grep "sh -x abc.sh" | grep -v grep | wc -l`; echo $check
1

Unable to understand why this difference, please help Smilie

Thanks
Sam
# 2  
Old 07-04-2013
I guess its because..

say when you run the ps -ef under backquotes it will run it under subshell and command would be fired and captured by same ps -ef so it will give 2 as output

I may not be 100% correct here
# 3  
Old 07-04-2013
The problem may be that sometimes the grep process is spotted too, which you are trying to handle. Could you consider using the -c flag of grep and neatening your code a bit?
Code:
check=`ps -ef|grep -c "sh -x abc.s[h]"`

The square brackets mean that the contents are a range of characters, in this case only h which might seem a little odd, but it means that your grep will not find itself. The count is a function of grep

Can you have a go with the above streamlined code and if it's still confusing, take the -c flag off and show us the output.



Robin
Liverpool/Blackburn
UK
This User Gave Thanks to rbatte1 For This Post:
Dheepak s
# 4  
Old 07-04-2013
@Robin, didn't work Smilie
still getting check=2 inside the program and 1 on command line

Code:
$ cat abc.sh
#!/bin/bash

check=0

check=`ps -ef|grep -c "sh -x abc.s[h]"`

echo "$check"

sleep 180

o/p
Code:
$ sh -x abc.sh
+ check=0
++ ps -ef
++ grep -c 'sh -x abc.s[h]'
+ check=2
+ echo 2
2
+ sleep 180

command line
Code:
$ ps -ef | grep "sh -x abc.s[h]"
sam     1234  5678  0 07:25 pts/13   00:00:00 sh -x abc.sh

---------- Post updated at 05:03 PM ---------- Previous update was at 04:59 PM ----------

@vidyadhar
I tried removing the shebang line and executing, still giving check=2
so may not be problem of changing shells

Code:
$ sh -x abc.sh
+ check=0
++ ps -ef
++ grep -c 'sh -x abc.s[h]'
+ check=2
+ echo 2
2
+ sleep 180

# 5  
Old 07-04-2013
Can you insert the lines:-
Code:
ps -fp $$
ps -ef|grep 'sh -x abc.s[h]'

above the active check=`ps .... and post the output. I'd like to see what is 'us' and what is not. There is no need to set the value of check to zero before you start. If grep -c does not match anything, it will return the value zero.



I'm a bit confused, I must admit. Smilie On AIX I get:-
Code:
RBATTE1>sh -x abc.sh
+ ps -fp 17864
UID        PID  PPID  C STIME TTY          TIME CMD
RBATTE1  17864 17757  0 12:54 pts/10   00:00:00 sh -x abc.sh
+ ps -ef
+ grep 'sh -x abc.s[h]'
RBATTE1  17864 17757  0 12:54 pts/10   00:00:00 sh -x abc.sh
++ ps -ef
++ grep -c 'sh -x abc.s[h]'
+ check=2
+ echo 2
2
+ sleep 180

.....yet on RHEL I get:-
Code:
RBATTE1> sh -x abc.sh          
+ ps -fp 2273350
     UID     PID    PPID   C    STIME    TTY  TIME CMD
 RBATTE1 2273350 1884412   0 13:01:50  pts/6  0:00 sh -x abc.sh 
+ grep sh -x abc.s[h]
+ ps -ef
 RBATTE1 2273350 1884412   0 13:01:50  pts/6  0:00 sh -x abc.sh 
+ + ps -ef
+ grep -c sh -x abc.s[h]
check=1
+ echo 1
1
+ sleep 180

.... and on HP-UX it's the same:-
Code:
RBATTE1> sh -x abc.sh
+ ps -fp 24145
     UID   PID  PPID  C    STIME TTY       TIME COMMAND
 RBATTE1 24145 24072  1 13:10:13 pts/tk    0:00 sh -x abc.sh
+ ps -ef
+ grep sh -x abc.s[h]
 RBATTE1 24145 24072  1 13:10:13 pts/tk    0:00 sh -x abc.sh
+ + ps -ef
+ grep -c sh -x abc.s[h]
check=1
+ echo 1
1
+ sleep 180


What OS are you using.



Thanks again,
Robin
# 6  
Old 07-04-2013
I am using

Code:
$ cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5.3 Beta (Tikanga)

below is the o/p you requested after inserting those two lines

Code:
$ sh -x abc.sh
+ ps -fp 18853
UID        PID  PPID  C STIME TTY          TIME CMD
sam     18853  5608  0 08:12 pts/13   00:00:00 sh -x abc.sh
+ ps -ef
+ grep 'sh -x abc.s[h]'
sam     18853  5608  0 08:12 pts/13   00:00:00 sh -x abc.sh
++ ps -ef
++ grep -wc 'sh -x abc.s[h]'
+ check=2
+ echo 2
2
+ sleep 180

# 7  
Old 07-04-2013
Funny enough - I placed a tee into the pipe, and - there are two processes! See:
Code:
check=$(ps -ef|tee xx|grep -c "[s][h] -x abc.sh")
less xx
...
userx   6061  4983  0 17:44 pts/2    00:00:00 bash -x abc.sh
userx   6062  6061  0 17:44 pts/2    00:00:00 bash -x abc.sh

one being an immediate subprocess of the other. Strange!
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