mjhjmtu

I'm trying to compose myself a bash script with the intent of it being used commonly in a terminal. It should start an application as a background process and discard it's stderr output. Here's what I got:

 for app in $@; do 
 $app 2>/dev/null
 done

It seemed to work just fine with bare applications started without parameters, like script.sh firefox gedit but failed to do the following:

script.sh "vlc video.mp4"

My question is: How can I enhance this basic script to handle applications which take parameters/files as their input? Maybe there already is a tool I can use?

There are two issues:

1. 
   

   The use of $@ without quotes.

   
   
   

   This would make the loop iterate over vlc and video.mp4 as two separate items, even if these were within the same quoted string in the invocation of the script.

   
   


2. 
   

   Using a command in a variable.

   
   
   

   If the command is anything more complicated than a single simple command, then this won't work. You would have to eval the given string instead.

   
   

Taking this into account, your script could look like

#!/bin/sh

for cmd do # or: for cmd in "$@"; do
 eval "$cmd" 2>/dev/null
done

Calling this as

./script 'echo "hello world"' 'vim "$HOME/.profile"' 'tr a-z A-Z <"$HOME/.profile" | grep -c EXPORT'

would first run echo "hello world", and when that finishes, it would open vim for editing the named file in that second command. The last command is more complex but handled by the fact that we use eval (it just changes all alphabetic characters to uppercase and counts the number of times the string EXPORT occurs in a file). It is run as soon as the vim session exits.

With this, you could even do

./script 'd=$HOME' 'ls "$d"'

i.e., set variables that are used in later commands. This works because the commands invoked by eval are run in the same environment as the script. This would not work if you start the commands as background tasks though, as the title of your question suggests.

You're currently telling your script to handle each parameter as a separate application. So you are running:

$ vlc

Then:

$ video.mp4

You should make your script more like this:

#!/bin/bash
$@ 2>/dev/null

Which, in my opinion, would be better suited as a function:

func_name() 
$@ 2>/dev/null

Note: this will only allow you to run one command at a time. I'm not sure if your original intent was to pass multiple commands at once to your script, if so I will delete.