Command Line – Differences Between ‘ & disown’ and ‘nohup & disown’

background-processbashcommand linenohup

This is my understanding about the usage of &, disown and nohup:

<command>: runs the process within the Terminal's current bash instance, in the foreground (i.e. the process is listed as a bash foreground job and stdin, stdout and stderr are still bound to the terminal); not immune to hangups;
<command> &: runs the process within the Terminal's current bash instance, in the background (i.e. the process is listed as a bash background job and stdin, stdout and stderr are still bound to the terminal); not immune to hangups;
<command> & disown: runs the process within the Terminal's current bash instance, in the background, but the process is detached from the bash's jobs' list (i.e. the process is not listed as a bash foreground / background job and stdin, stdout and stderr are still bound to the terminal); immune to hangups;
nohup <command> & disown: runs the process within the Terminal's current bash instance, in the background, but the process is detached from the bash's jobs' list (i.e. the process is not listed as a bash foreground / background job and stdin, stdout and stderr are not still bound to the terminal);immune to hangups;

So, aside from nohup <command> & disown blocking stdin and redirecting stdout and stderr to nohup.out by default, it seems to me like it can be considered totally equivalent to <command> & disown.

Is the above all correct? Any misconception?

Best Answer

Your understanding is basically correct. Both disown and nohup are used to allow you to exit a running shell session without stopping running jobs. Some clarifications:

There's no reason to run nohup command & disown, nohup will already disown it for you.
nohup is defined by POSIX while disown is not. This means that while many shells (e.g. bash, zsh, ksh) have it, others (for example tcsh, csh, dash and sh) won't have it.
disown can be used after a command has been launched while nohup must be used before.

As far as I can tell, the actual effect of the two commands is the same. They each have features that the other lacks (see help disown and man nohup) but their basic function is the same, yes.

For a far more detailed discussion of these tools and the differences between them, have a look at the answers here:

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Command Line – Bash History Keyboard Shortcut for !*

If you look at the output of the following command:

bind -l

or better to:

bind -l | grep arg

you can see that doesn't exist any readline function for all arguments like is, for example, yank-last-arg for last argument - which can insert last argument to the previous command (the last word of the previous history entry). So, if such a function doesn't exists, most probably doesn't exist a shortcut to accomplish what you wish.

Let's try to crate one approached to your request...

First, look for example at the output of the following command:

bind -p | grep yank-nth-arg

The output is:

"\e\C-y": yank-nth-arg

and can be translated as follow: yank-nth-arg (which insert the first argument to the previous command - with an argument n, insert the nth argument from the previous command) is bound to Alt+Ctrl+y.

In the same way can be interpreted any line from the output of bind -p command.

Now play attention at the following scenarios:

If you set the following binding:
```
bind '"\ea": "\e2\e."'
```
Alt+A will be mapped to Alt+2Alt+. which is mapped to insert the second argument of the previous command. So, after when you press Alt+A, the second argument of the previous command is inserted in the current command.
If you set:
```
bind '"\ea": "\e1\e. \e2\e."'
```
After when you press Alt+A, the first two arguments of the previous command is inserted in the current command. If the number of the arguments from the previous command is maximum 2, of course all of the previous command is inserted in the current command.
If you set:
```
bind '"\ea": "\e1\e. \e2\e. \e3\e."'
```
After when you press Alt+A, the first three arguments of the previous command is inserted in the current command. If the number of the arguments from the previous command is maximum 3 (as in your case), of course all of the previous command is inserted in the current command.
And so on.

For first 10 arguments, you can use:

bind '"\ea": "\e1\e. \e2\e. \e3\e. \e4\e. \e5\e. \e6\e. \e7\e. \e8\e. \e9\e. \e1\e0\e."'

And I think that this is long enough as far as I don't use too often commands with so many arguments.

To make it persistent, add the following line line to your ~/.inputrc file:

"\ea": "\e1\e. \e2\e. \e3\e. \e4\e. \e5\e. \e6\e. \e7\e. \e8\e. \e9\e. \e1\e0\e."

In this example I chose Alt+A to insert all arguments (if the number of arguments is not greater than 10) of the previous command, but you can chose any other combination you with by replacing in the previous command the \ea string.

Resources:

Commands For Manipulating The History
help -m bind
BASH - How to use arguments from previous command?

Best Answer

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