Linux – Is “ps -u” Really a Bad Syntax

linuxpsshell

IMHO ps -u shows a very useful output, much better than ps -u $USER:

$ ps -u
Warning: bad syntax, perhaps a bogus '-'? See /usr/share/doc/procps-3.2.8/FAQ
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
elastic   234897  0.0  0.0 105980  1336 pts/2    S+   Oct10   0:00 /bin/bash ./run.sh collector-json-1.conf
elastic   234899 48.7  7.1 10087120 4433104 pts/2 Sl+ Oct10 2804:11 /usr/java/jdk1.7.0_09_x64/bin/java -Xmx6144m -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -Djava.awt.headless=true -XX:CMSInitiatingOccupancyFraction=75 -XX:+UseCMSInitiatin
:

compared to

$ ps -u $USER
    PID TTY          TIME CMD
 234897 pts/2    00:00:00 run.sh
 234899 pts/2    1-22:44:04 java
:
  1. But, why is it "bad syntax"? /usr/share/doc/procps-3.2.8/FAQ doesn't help much.
  2. What would be a "proper syntax" to achieve the exact same output?

In case it's important:

$ uname -a
Linux h22k34.local 2.6.32-042stab044.17 #1 SMP Fri Jan 13 12:53:58 MSK 2012 x86_64 x86_64 x86_64 GNU/Linux

Best Answer

The correct syntax, which returns the same output, would be:

ps u

There is a good reason why modern syntax for ps is a mess. Historically, there were two incompatible version of ps. Options with a leading dash were inherited from the AT&T Unix version of ps. Options without a leading dash were inherited from BSD. The version of ps that Linux distributions generally use is GNU which has merged both sets of options together, as well as added its own set of options that start with a leading double-dash.

Thus, ps u is BSD-style and ps -u $USER is AT&T-style. The fact that GNU ps allows you to run ps -u and, other than the warning, get the same output as ps u shows that GNU is attempting to make the best of a bad situation.

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