Updates basics_of_linux.md

This is a huge chapter. I could divide it up in many subchapters but I like to have it all at one place so I can just do `ctr-f`, and search for whatever I am looking for.

## The Shell - Bash

## 1. The Shell - Bash

The shell, or the terminal is a really useful tool. Bash is the standard shell on most Linux distros.

`ls -ltr` - Sort list by last modified. -time -reverse

`file` - Show info about file.

`file` - Show info about file. What type of file it is. If it is a binary or text file for example.

`cat` - Output content of file.

`less` - Output file but thest little bit at a time

`less` - Output file but just little bit at a time. Use this one. Not `more`.

Use `/searchterm` to search. It is the same command as in vim. `n` to scroll to next search result. Press `q` to quit.

`more` - Output file but just little bit at a time. `less` is better.

### Working with files

`rmdir` - Remove empty directory

### A little bit of everything

**history**

Show commands history

`history` - Show commands history

**sudo**

`sudo`

List what rights the sudo user has.

Sudo config file is usually **/etc/sudoers**

## Finding files

### Finding files

There are mainly three ways to find files on Linux: **find**, **locate**, and **which**.

#### Find

There are mainly three ways to find files on linux. **Locate**, **find** and **which**.

Find is slower than locate but a lot more thorough. You can search for files recursively and with regex and a lot of other features.

```

# This will send all permissions denied outputs to dev/null.

find / -name file 2>/dev/null

```

### Locate

#### Locate

Locate is really fast because it relies on an internal database. So in order to have it updated you need to run:

```

updatedb

sudo updatedb

```

Then you can easily find stuff like this:

locate filename

```

### Which

#### Which

Which searched the directories that are defined in your $PATH variable.

Outputs the path of the binary that you are looking for. It searches through the directories that are defined in your $PATH variable.

### Find

```bash

which bash

# Usually outputs: /bin/bash

```

## 2. Editing text

First let's just clear out something about **standard streams**. Standard streams are the streams that are used to interact between the human computer-user and the machine. There are three standard streams: standard input (stdin), standard output (stdout), and standard error (stderr).

Find is slower but a lot more thorough. You can search for files recursively and with regex and a lot of other features.

### Stdin

Stdin is the data that gets inputed into the program. An example of a program that requires stdin data is `cp`. In order for the program to do anything it needs input data. For example `cp file1 copy_of_file1`. Here `file1` and `copy_of_file1` is the stdin.

### Stdout

Stdout is the data that get ouputed from the program.

For example, when you use the command `cat file1` that data/text that gets outputed is the stdout. Not all programs have stdout. For example when you use `mv` or `cp` successfully you get no stdout back from the program.

### Stderr

Stderr is the stream used for outputting error messages. So if a program fails for whatever reason. For example, if we try to copy a file that does not exist, this will be the stdrr output:

```

# This will send all permissions denied outputs to dev/null.

find / -name file 2>/dev/null

cp thisfiledoesnotexist aaaaaaaaaa

cp: cannot stat 'thisfiledoesnotexist': No such file or directory

```

## 2. Text-fu

* [https://linuxjourney.com/lesson/stderr-standard-error-redirect](https://linuxjourney.com/lesson/stderr-standard-error-redirect)

### cut