Comments on: Shelling scripting is a necessary skill

By: Ben Hartshorne

Ben Hartshorne — Thu, 19 May 2011 04:11:14 +0000

The trick of using “grep [a]pplication” works because it alters the line representing ps to a point where the regex no longer matches.

In other words, when you put “grep [a]pplication” in your pipe, the ps output shows exactly that (my test uses grep -v so I can see it):
ben 8886 17330 0 21:07 pts/17 00:00:00 grep -v [a]pplication

The regex of [a]pplication will match application, but you would have to escape the brackets for it to match [a]pplication. Because of that, the grep line no longer matches the regex and doesn’t appear.

By: MK

MK — Thu, 24 Mar 2011 02:29:21 +0000

How does this trick of omitting grep from the results of grep work ?

pid = $(ps -ef | grep [a]pplication)

Thanks!

By: timeout – new coreutils command

timeout – new coreutils command — Sat, 15 Jan 2011 18:46:04 +0000

[...] 7.0 Beta (2008-10-05) is an exceedingly useful command. Often I write a script which needs to run a particular command for a period of time and then stop and restart. Before timeout this was quite painful. Some commands such as nc (netcat) [...]

By: Phil

Phil — Mon, 04 Oct 2010 22:41:51 +0000

To simplify things:

pid=$(ps -ef | grep application | egrep -v grep | awk ‘{print $2}’)

Could be rendered:

pid=$(ps -ef | grep [a]pplication | awk ‘{print $2}’)

By: pat

pat — Thu, 29 Apr 2010 20:44:33 +0000

i’m sure you’d fall in love with /usr/bin/pgrep if you knew it…

By: Peko

Peko — Wed, 24 Mar 2010 23:37:35 +0000

“there was thoughts of automatically restarted the application to fix the issue at hand”

Do you mean “restarting”? (not “restarted”)

By: Peko

Peko — Wed, 24 Mar 2010 23:36:21 +0000

“there was thoughts of automatically __restarted__ the application to fix the issue at hand”

Do you mean “restarting” ?

By: Peko

Peko — Wed, 24 Mar 2010 23:30:57 +0000

This :
pid=$(ps -ef | grep application | egrep -v grep | awk ‘{print $2}’)

Could be simplier:
pid=$(pgrep application)

Or at least more effective if “pgrep” is unvailable:
pid=$(ps -ef|grep [a]pplication|awk ‘{print $2}’)

Using the good ol’ trick preventing “grep” from listing itself.

By: Brock Noland

Brock Noland — Wed, 24 Mar 2010 17:53:07 +0000

Just so if the strace fails, the script does not go berserk. A “safety” mechanism of sorts.

By: James

James — Wed, 24 Mar 2010 17:12:51 +0000

What is the purpose of the “while sleep 60″ line?