Comments on: Quick Unix Tips

By: Giovanni Caristi

Giovanni Caristi — Sat, 27 Oct 2007 15:19:40 +0000

In Leopard, ps -aux won’t work anymore, as I painfully discovered.
A “ps aux” wrapper is provided:

The biggest change is in the interpretation of the -u option, which now displays processes belonging to the specified username(s).
Thus, “ps -aux” will fail (unless you want to know about user “x”). As a convenience, however, “ps aux” still works as it did in Tiger.

By: What is Unix?

What is Unix? — Thu, 15 Mar 2007 08:36:06 +0000

To what audience are these ‘tips’ intended? Listing touchm which one almost never uses, without listing the handy pwd seems unusual. If this is meant as an introduction (and by including cd it must be), then there are some vital commands that have been left out. cat, vi, ls without the redirection of output…

By: Eric F Crist

Eric F Crist — Wed, 24 Jan 2007 05:53:15 +0000

In addition to above, if you use the following command, it will run the first, and only run the second if the first exited ‘0′ (zero), meaning successful:

command && command

You can do this as many times as you want:

touch test.txt && touch test.txt2 && touch text.txt3

If you didn’t have write perms to the directory you’re trying to create the files in, the first would exit 1, and all other commands would simply not be executed.

By: Michael

Michael — Fri, 19 Jan 2007 17:08:51 +0000

command1 | command2

Does not run command1 followed by command2. The pipe symbol ‘|’ “pipes” the output of command1 into the input of command2. As such, both command1 and command2 run at the same time.

For example: ps ax | grep Mail

Runs “ps” and then pipes the output of “ps” into “grep”. Grep finds any line matching the first argument. In this case, any lines output from ps that contain the word “Mail” will be output by grep.

If you want to run one command followed by another command, the correct syntax is:

command1 ; command2

By: Clair

Clair — Fri, 19 Jan 2007 14:37:49 +0000

ps aux
is the proper syntax.

ps awwx

On the Mac, this command will format the process list so you can actually read the entire line of the process.

For example if your terminal window is only 80 columns wide, ps aux will chop off any characters past the 80 column mark will be cut off. This is not very useful if your path is longer than the screen is wide (including the rest of the process information).

By: weldon

weldon — Fri, 19 Jan 2007 02:21:35 +0000

“touch” will also update the last modified date of a file if it already exists (which is where the name comes from). I know because I got in a bit of trouble with our senior UNIX admin at college when I wrote a script that would wake up every few hours and “touch” all the files in my temp directory so that they wouldn’t get deleted by another chron job that cleared out old files.

By: Wieger

Wieger — Thu, 18 Jan 2007 22:00:54 +0000

Wow cool to see my stuff on the website. I shall try to find some more nice things under the hood of OS X.
I hope you like it:)

By: mdmunoz

mdmunoz — Thu, 18 Jan 2007 21:11:55 +0000

Ugh. Beaten.

By: Jason

Jason — Thu, 18 Jan 2007 21:11:45 +0000

Grr. The && above should just be &&

By: Jason

Jason — Thu, 18 Jan 2007 21:11:07 +0000

Grr… The “&&” above should just be “&&”

By: mdmunoz

mdmunoz — Thu, 18 Jan 2007 21:10:48 +0000

Can’t you get to the home directory by entering cd with no arguments?

By: Jason

Jason — Thu, 18 Jan 2007 21:10:20 +0000

A couple embellishments: The ~/ is not necessary in the first example; cd by itself will change the working directory to the current user's home. The last example is more complicated than the text lets on. The | character creates what is called a pipe. The pipe redirectes the output (stdout) of the first command into the input (stdin) of the second. See the Wikipedia "Pipeline" entry for a decent introduction. Pipes are great for things like ps -aux | grep Finder (which will find the Finder process). If all you want to do is run commands in succession then use &&, which only runs the second if the first is successful.