if pgrep apache; then echo "oliver"; fi
This will echo oliver if the command pgrep apache is not empty. I want to do the reverse. If the the command pgrep apache returns an empty string, run a command.
3 Answers
if ! pgrep apache; then echo "oliver"; fi
1 Comment
onassar
This was exactly what I was looking for. Thanks DigitalRoss.
Try doing this :
pgrep &>/dev/null apache || echo "foobar"
or :
if ! pgrep &>/dev/null apache; then echo "foobar"; fi
! stands for NOT
this is not based on the output of the command but if the command whas true or false.
In shell, when the return code of a command is 0, it's considered true, if more than 0, it's false. You can check this return code with the variable $?, example :
ls /path/to/inexistant/file
echo $?
1 Comment
William Pursell
Do not use
&>. The grammar is ambiguous: bash will treat it the same as >/dev/null 2>&1, while dash will treat it as & > (it will run the process in the backround, and then truncate /dev/null)I'm unsure of the context but presuming you want to do something a particular process is or is not found.
bash-3.2$ pgrep -q bash && echo "bash was found"
bash was found
bash-3.2$ pgrep -q XXXbash || echo "XXXbash was NOT was found"
XXXbash was NOT was found
pgrep apacheis not empty'. Rather, it is executed becausepgrepreturns successfully. In this case, the command being successful and the command generating some output are equivalent, but this is a common source of confusion.