shell: different shells and for loops

master
tiyn 2 years ago
parent 8a80618378
commit b893c73571

@ -3,20 +3,95 @@
A shell is a command-line interpreter that provides a command-line interface to A shell is a command-line interpreter that provides a command-line interface to
interact with the many unix-like system. interact with the many unix-like system.
## Change the standard shell ## Unix Shells
The Shell in some distributions is made up by a POSIX compliant mode of bash. The following is a list of Unix shells that are POSIX compliant.
Problem with that is the speed.
A shell like dash would be much faster.
This is a guide on how to persistently change the symlink /bin/sh from bash to
dash.
- `yay -S dash` - Install dash - [Bash](https://www.gnu.org/software/bash/) is the GNU Projects shell.
- `sudo ln -sfT /bin/dash /bin/sh` - link /bin/sh to dash It is probably the most used and well known shell.
- `sudo vim /usr/share/libalpm/hooks/bash-update.hook` - setup a hook to avoid - [DASH](http://gondor.apana.org.au/~herbert/dash/) is a small implementation of
bash resetting the symlink `/bin/sh`. It is significantly faster than Bash and it is recommende to set
DASH to be [the system shell](#changing-the-system-shell-binsh).
- [Zsh](https://www.zsh.org/) is a shell designed to be interactive but also a
powerful scripting language. It is often set to be the
[default user shell](#changing-the-default-user-shell) because of its user
friendliness and a more features like the possibility for
[syntax highlighting](https://github.com/zsh-users/zsh-syntax-highlighting)
and [auto suggestions](https://github.com/zsh-users/zsh-autosuggestions).
## Disown a Command ## Usage
This section addresses various different functions by and actions that can be
taken with shell commands.
### For Loops
For loops can be especially useful when scripting.
A function could be called on all the files in a directory.
The following command shows the basic functionality and syntax of a for loop in
a POSIX compliant shell.
The command appends `-1` to all files in the current working directory.
It consists of the loop structure that cycles through all files `*`.
and appends `-1` using `mv "$f" "${f}-1"`.
The command aswell as the scope could be change to only cycle through specific
filetypes or use another command.
```sh
for f in *
do mv "$f" "${f}-1"
done
```
This command can also be shortened to a single line by using `;` like the
following shows.
```sh
for f in *; do mv "$f" "${f}-1"; done
```
### Changing the Default User Shell
The default user shell can be changed with the following command.
Change `<path to shell>` according to the shell to set.
For [ZSH](#unix-shells) this would be `/bin/zsh`.
```sh
chsh -s <path to shell>
```
### Changing the System Shell /bin/sh
The system shell in some distributions is made up by a POSIX compliant mode of
Bash.
This can be slow at times and a shell like
A shell like [DASH](#unix-shells) would be much faster.
This is a guide on how to persistently change the symlink /bin/sh from Bash to
DASH.
Run the following commands to install and link `/bin/sh` to the DASH shell.
```sh
yay -S dash
sudo ln -sfT /bin/dash /bin/sh
```
Afterwards create the file `/usr/share/libalpm/hooks/bash-update.hook` and fill
it with the following text.
```txt
[Trigger]
Type = Package
Operation = Install
Operation = Upgrade
Target = bash
[Action]
Description = Re-pointing /bin/sh symlink to dash...
When = PostTransaction
Exec = /usr/bin/ln -sfT dash /usr/bin/sh
Depends = dash
```
### Disown a Command
This section is based on a guide by This section is based on a guide by
[baeldung](https://www.baeldung.com/linux/detach-process-from-terminal). [baeldung](https://www.baeldung.com/linux/detach-process-from-terminal).
@ -25,7 +100,7 @@ Commands that are detached from a shell will not terminate upon its closure.
A command can be disowned simply by appending `& disown` at the end of it. A command can be disowned simply by appending `& disown` at the end of it.
It will then provide the PID of the command that got disowned. It will then provide the PID of the command that got disowned.
## Silencing a Command ### Silencing a Command
This section is based on a guide by This section is based on a guide by
[baeldung](https://www.baeldung.com/linux/silencing-bash-output). [baeldung](https://www.baeldung.com/linux/silencing-bash-output).

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