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Use dash for scripts instead of bash; Fix typo

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TrudeEH
2025-04-23 15:09:15 +01:00
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commit f12f6ce973
3 changed files with 25 additions and 17 deletions
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content/notes/firewall.md
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@@ -9,7 +9,7 @@ tags:
author: TrudeEH
showToc: true
---
A firewall monitors and controls all incoming and outgoing network traffic, and can be implemented in the hardware or software level.
A firewall monitors and controls all incoming and outgoing network traffic, and can be implemented at the hardware or software level.
## See All Open Ports

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content/notes/linux/index.md
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@@ -206,11 +206,11 @@ The GPU still has a device file, which is used by the Kernel's DRM and Mesa, but
## Shell (`bash`)
The kernel by itself isn't intractable, so a shell is needed for the user to be able to execute programs and run commands. Bash is not only a prompt, but also an interpreter for its own programming language, which can be used to write scripts and automate tasks.
The kernel by itself isn't intractable, so a shell is needed for the user to be able to execute programs and run commands. `bash` is not only a prompt, but also an interpreter for its own programming language, which can be used to write scripts and automate tasks.
### Commands
Bash performs actions through commands. A shell command consists of the command itself, followed by its arguments.
`bash` performs actions through commands. A shell command consists of the command itself, followed by its arguments.
```bash
command "arg1" "arg2"
@@ -218,14 +218,18 @@ command "arg1" "arg2"
If the first word of a command is a reserved word, bash handles the command, otherwise, it searches for an executable on the system's `$PATH`, a list of directories where a binary could be located.
### Bash Scripts
### Shell Scripts
While `bash` is typically used as the login shell, it is slow for script execution. For this reason, many distributions (such as Debian) use `dash` to run `sh` scripts (symlink `/bin/sh` to `/bin/dash`), which is a faster alternative to `bash`, designed specifically to execute scripts and to be strictly POSIX compliant.
When writing scripts, it's a good practice to follow the POSIX standard, to make them compatible with most shells, older systems, and different distributions, while taking advantage of `dash`'s faster performance. Keep in mind that `dash` is not `bash` compatible, and some `bash` commands might not work on `dash`.
Example `script.sh`:
```bash
#! /bin/bash
#! /bin/sh
echo "Bash Script"
echo "Shell Script"
```
Execute the script:
@@ -235,15 +239,15 @@ chmod u+x script.sh # Give the script execution permission (to its owner)
./script.sh # Run the script
```
After writing a script, use `shellcheck` to check for issues.
### Learning
There are some commands available to search for documentation:
```bash
tldr command # Examples of how to use the command (external tool)
help command # Short documentation for the command
man command # Full documentation for the command
man bash # Bash documentation; Includes most built-in commands
tldr command # Examples of how to use the command (external tool)
help command # Short documentation for the command
man command # Full documentation for the command
man dash # Dash documentation; Includes most built-in commands
```
> To get started, use `help` by itself, which provides a list of the built-in commands available in bash.
@@ -253,6 +257,8 @@ For example, suppose you want to learn how to write an `if` statement in `bash`:
![Pasted image 20250422123058](../../Pasted%20image%2020250422123058.png)
As suggested by `tldr`, to see all possible conditions, use the `man test` command.
> If you are writing scripts using `dash`, it's recommended to read the `dash` manual instead: `man dash`. The `if [[ ]]` syntax is exclusive to `bash`, for example, and should be replaced with `if [ ]` to use with `dash`.
### Compiling
Dependencies:
@@ -286,6 +292,8 @@ sudo apt install ../bash*.deb
Bash includes a set of *builtins*: Command-line utilities that come within bash itself. However, these are very limited, and to actually make the computer useful, more programs are needed.
> To learn more about a program, use: `man program_name`.
### Coreutils
*Coreutils* are a collection of small command-line utilities, which are essential for text, file and shell manipulation.