Why are different results returned

[uk_jih]

Hello all,

If I enter the command:

ps -ef | grep ./DBTest | grep -v $$ | wc -l

I get "0" as the output

If I enter xxx=`ps -ef | grep ./DBTest | grep -v $$ | wc -l` or
xxx=$(ps -ef | grep ./DBTest | grep -v $$ | wc -l)

$xxx is set to 1

I am trying to use this logic to allow a program (called DBTest) to only run if there is not a program called DBTest already running.

My suspicion is it is something to do with $$

Cheers
John

[lomcevak]

This is only a guess but the 'grep -v $$' will exclude any line with that number which is the PID. If the ps output for ./DBTest has that number somewhere in its line then that line will be excluded as well. Try using the grep '-w' option.

ps -ef | grep \./DBTest | grep -v -w $$ | wc -l

Also '.' means match any character to grep so escape it as I did to search specifically for a dot.