Strange behavior returning incorrect count

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10-02-2015

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As said earlier, pipes do a fork/exec. And while the exec is not yet ready there is a cloned shell. This is a race condition.
To avoid the race conditions you must avoid sub-shells and pipes and maybe even calling external programs.
The best thing is pgrep. Unfortunately AIX does not have it.
cjcox and Aia solutions combined is maybe good enough:

Code:

!/bin/ksh
ps | grep -c "tt11[.]ksh"
count=$(ps | grep -c "tt11[.]ksh")
echo ""
echo "$count"
echo "----"

--
Someone mentioned the lockfile method.
If the purpose is to prevent multiple instances to run, then indeed the lockfile method seems better than the process method.

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suspend

suspend(1)							   User Commands							suspend(1)

NAME

       suspend - shell built-in function to halt the current shell

SYNOPSIS

   sh
       suspend

   csh
       suspend

   ksh
       suspend

DESCRIPTION

   sh
       Stops the execution of the current shell (but not if it is the login shell).

   csh
       Stop the shell in its tracks, much as if it had been sent a stop signal with ^Z. This is most often used to stop shells started by su.

   ksh
       Stops the execution of the current shell (but not if it is the login shell).

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), kill(1), ksh(1), sh(1), su(1M), attributes(5)

SunOS 5.10							    15 Apr 1994 							suspend(1)

Shell Programming and Scripting