CODEWITHSUNDEEP
bash
tatyana
tatyana

Reputation: 55

bash background operator & error with AND operator &&

If I try to execute this code in bash shell will work fine:

date && echo "hello world"

But if I want to run date in background and then use echo it does not work:

date & && echo "hello world"

Edit:

The final task is run a script that connect to vpn:

# openvpn /etc/openvpn/client/my_vpn.ovpn

And if this work that appear a message. The problem is that vpn command is always running and the next command not show. Ej:

# openvpn /etc/openvpn/client/my_vpn.ovpn  && notify-send "VPN connect"

I tried:

# openvpn /etc/openvpn/client/my_vpn.ovpn  & && notify-send "VPN connect"

The second message never run, so I tried run a more simple command for test with date.

Upvotes: 0

Views: 784

Answers (3)

oguz ismail
oguz ismail

Reputation: 50750

Because just like semicolon and line break characters, ampersand is a command separator too.

date ; && echo 'hello world'

and

date
&& echo 'hello world'

won't work either.

If you did

{ date & } && echo 'hello word'

however, it'd work. But that doesn't make any sense, asynchronous commands (e.g. date &) always return zero.

Upvotes: 0

Demi Murych
Demi Murych

Reputation: 139

Need more information about your task. Because the exact answer depends on the conditions that you did not say.

For example:
If your task is to run a code in the background and, if it succeeds, print a message to standard output, then this is done like this:

{ date && echo "hello world"; } &

Or
If you have a task, run something in the background and later get the result, then this is done like this:

coproc dateDoneUndone { 
    date && {echo "Done"; } || {echo "UnDone"; } 
}

# some code

readarray -u ${dateDoneUndone[0]} ans; 
echo "Result: ${ans[@]}"

In order to better understand what this code does, you need to read documentation about redirections, job control and coprocesses.

Upvotes: 1

choroba
choroba

Reputation: 241858

If you run a command in the background, what would be the meaning of &&? You don't wait for the command to finish, so you don't know whether it was successful or not. Just use the & operator alone to separate the commands:

date & echo 'hello world'

Upvotes: 1

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