Command-Line Processes – Do All Programs Need Shell Access?

bashcommand lineguikernel

I have seen somewhere that "bash is used to communicate with the Linux kernel."

Is it applicable only to the terminal? Or does every program (including programs which has GUIs) have to go through the shell to complete the process they willing to make?

(Consider we are coloring a photo. How does bash know what we are doing? Is there a third party between gimp and bash to convert them to bash?)

It would be really helpful if can you take an example to explain 🙂

Best Answer

Nope. Only users have to go through a shell to communicate with the Kernel. Applications use APIs.

For example, if I want to delete a file, I have to use one shell or the other, and then an application to delete the file:

With a Command-Line Interface (CLI) shell, such as bash, I can use the rm command to delete the file.
With a GUI shell (like Unity, or GNOME Shell), I can use something else, such as the File Manager to delete the file. The GUI shell does not, in turn, need to use a CLI shell.

Both the File Manager and rm in turn may use the unlink(3) (or the higher level remove(3)) function (or system call) to do the actual work.

Related Solutions

Default Shell – How to Make ZSH the Default Shell

Just using chsh:

chsh -s $(which zsh)

without sudo should work. If you use sudo it will change the shell not for your working user but for root

Finally, log out of your computer and log back in.

Troubleshooting:

Do you have zsh installed (ii)? dpkg -l zsh
Is your shell set to zsh? Last field of grep $USER /etc/passwd
Is Zsh a valid login shell? grep zsh /etc/shells

Make a Sound Once a Process is Complete – Command Line Guide

There are at least three command line ways to accomplish this by putting the suiting command at the end of your script you may invoke for your lengthy process:

The "classical" way to play a sound is to use beep.

Beep will make a tone through the PC speaker. However this will not work in all cases (e.g. in my system PC speakers are completely disabled) You may have to remove pcspkr from /etc/modprobe/blacklist.conf and load the pcspkr kernel module:
```
sudo sed -i 's/blacklist pcspkr/#blacklist pcspkr/g' /etc/modprobe.d/blacklist.conf
sudo modprobe pcspkr
beep [optional parameters]
```
We can also play any sound file in wav format using aplay (installed by default):
```
 aplay /usr/share/sounds/alsa/Side_Right.wav
```
Another way is to use the pulseaudio command line interface to enable playback of any sound files your system (in libsndfile) recognizes on the default audio output:
```
  paplay /usr/share/sounds/freedesktop/stereo/complete.oga
```

We can use default sound files from /usr/share/sounds/, or any other sound file we may have in a different location.

Just to have mentioned it, there is another nice way to achieve this by misusing espeak, which is installed by default in Ubuntu <= 12.04. See, or rather hear the following example:

#! /bin/bash

c=10; while [ $c -ge 0 ]; do espeak $c; let c--; done; sleep 1 ## here lengthy code
espeak "We are done with counting"

In Ubuntu >= 12.10 Orca uses speak-dispatcher. We can then install espeak, or alternatively use spd-say "Text".

Best Answer

Related Solutions

Default Shell – How to Make ZSH the Default Shell

Make a Sound Once a Process is Complete – Command Line Guide

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