Menu
Why the following if statement succeeds ?
if $(ps aux | grep -q "bla bla") ; then echo "found" ; fi
997
The ps aux | grep x command gives "better" results than pgrep x essentially because you are missing an option with the latter. Simply use the -f option for pgrep to search the full command line and not only the process name which is its default behavior, eg: pgrep -f php5.
$(...) is an expression that starts a new subshell, whose expansion is the standard output produced by the commands it runs. This is similar to another command/expression pair in bash : ((...)) is an arithmetic statement, while $((...)) is an arithmetic expression. Follow this answer to receive notifications.
The POSIX and UNIX standards require that "ps -aux" print all processes owned by a user named "x", as well as printing all processes that would be selected by the -a option. If the user named "x" does not exist, this ps may interpret the command as "ps aux" instead and print a warning.
Because the grep process itself is being returned by ps. You can "trick" grep to not match itself by surrounding one of the search characters in a character class [ ] which doesn't change the functionality: Just do:
if ps aux | grep -q "[b]la bla" ; then echo "found" ; fi Also, the use of process substitution $() is unnecessary. The if will work on the success of the last command in the pipe chain, which is what you want.
Note: The reason the character class trick works is because the ps output still has the character class brackets but when grep is processing the search string, it uses the brackets as syntax rather than a fixed string to match.
144
If you grep the output from ps aux, you will always get a process showing your previous command. To fix this, you can pipe the output to grep twice, once to remove line with "grep" in it, and again for the process your looking for.
ps aux | grep -v "grep" | grep "Finder"
23
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
