Most ps-grep pipelines are underspecified (including all instances in this thread). Consider the following:
Quote:
Originally Posted by Yoda
Code:
ps -ef | grep [p]rocessName
The pattern is evidently intended to match only a command name, but then why is it allowed to match any portion of a full listing? With such a promiscuous approach, usernames, command line arguments, and ps headers can trigger a false positive.
Even if the match is restricted to the command name, if the pattern isn't anchored at both ends, substring matches could cause false positives.
These have the added limitation of not being capable of searching for a grep command.
If I were going to use ps to portably test for the existence of a process whose command name is exactly cmdName, it would look something like this:
Code:
ps -eo comm= | grep -qFx cmdName
If portability isn't a concern, on a Linux system one could also use:
Code:
ps -C cmdName >/dev/null
Quote:
Originally Posted by hanson44
The other methods suggested (pgrep and [p]attern)are fine too. But I don't think they are "better". The other methods are (a little) shorter, so that's a small advantage. But one method is subject to failure if pgrep not present, the other admittedly clever method is not obvious to many users why it works, can be confusing to many users. I would normally use the simple way you presented.
It's not just about being concise; pgrep makes it simple to do the right thing. Its default behavior is to match against the command name only (args are excluded unless -f is provided). Further, a pgrep instance also excludes itself from the list of results, making it trivial to search for other instances of pgrep.
While it may not be available on the OP's system, pgrep has been widely available for about 5 years now on Solaris, HP-UX, Linux, OpenBSD, NetBSD, FreeBSD, OS X, and others.
Regards,
Alister
Last edited by alister; 04-24-2013 at 03:30 AM..
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04-24-2013
But I don't think they are "better". The other methods are (a little) shorter, so that's a small advantage. But one method is subject to failure if pgrep not present, the other admittedly clever method is not obvious to many users why it works, can be confusing to many users. I would normally use the simple way you presented.