BASH- Run MPlayer if either there are no users on display :0 or if there is more than one argument

Question

This is the script I currently have-

#!/bin/bash
if["$#" == "2" OR who | grep ":0" == ""]
    export DISPLAY=:0
    xset dpms force on
    mplayer -fs $1.mp4
fi

It doesn't work.

Thanks for your help.

Answer 1

You should spend some time reading man test, it looks to me like you've got several problems here:

if [ "$#" = "2" -o -z "$(who | grep ':0')" ]; then

• Notice the space after the [.
• Notice the one equal sign for string compare.
• Notice that -o is the OR operator.
• Notice the -z for testing against the empty string.
• Notice the $(...) to execute the who command.
• Notice the space before the ].
• However, who prints out times and grep is going to match a lot of false positives against HH:MM:SS. You may want to improve your match.
• And as other answers note, you should probably check the success of the $(who|grep), rather than testing for empty string output.

In the future, more detail than "it doesn't work" is preferred ;)

Answer 2

In BASH, the test for NULL is -z , e.g if [ -z "$NAME" ]; then .... However, you can just as easily use the exit status from grep instead:

root@tpost-desktop:/usr/src# who | grep :0
tpost    tty7         2010-05-23 09:16 (:0)
root@tpost-desktop:/usr/src# echo $?
0

root@tpost-desktop:/usr/src# who | grep :123
root@tpost-desktop:/usr/src# echo $?
1

If grep did not find what you asked, it will exit with a non-zero status. So you could do something like:

who | grep :0 >/dev/null 2>&1
if [ $? = 0 ]; then
   USING_DISPLAY=1
else
   USING_DISPLAY=0
fi

Then test the value of USING_DISPLAY , play the movie if its 0

Answer 3

There needs to be a space after the if, after the [ and before the ']'.

#!/bin/bash
if [ "$#" == "2" ] || ! who | grep '(.*:0.*)$' > /dev/null 2>&1
then
    export DISPLAY=:0
    xset dpms force on
    mplayer -fs $1.mp4
fi