Title

# Hands on working with **bash**
---

## About shells

- `shell` = command line interface to computer.

- `bash` = one of the most used shells

- other shells: `zsh`, `ksh`, `sh`, ...

---
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## First steps

First simple command:
```bash
$ pwd
/home/schmittu
```

The `$` is called **prompt** and can look different, e.g

```bash
[schmittu@slab1vrt ~]$
```

Here the prompt contains the user before the `@`, followed by the "hostname" and `~` indicates the home
folder.

The output after `pwd` is the *current working directory* which on Linux systems usually
is `/home/<username>`.

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## Paths

Text like `/home/schmittu` describing the location of a file or folder is called a *path*.

- The first `/` relates to the root of the file system and then folders separated by `/`
the last entry is a file or folder.

- Such a path starting with `/` is also called an *absolute path*.

- A path not starting with `/` is called an *relative path* which is relative
  the current working directory

- `.` and `..` are also paths, the first is a shortcut for the current working
  directory, the `..` refers to the parent of the current working directory.

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## Changing the current working directory

`cd` = "change directory"

```bash
$ cd /tmp
$ pwd
/tmp
```

```bash
$ cd .
$ pwd
/tmp
```

```bash
$ cd ..
$ pwd
/
```

A simple `cd` changes to the home folder

```bash
$ cd
$ pwd
/home/schmittu
```

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## Listing files

ls = "list files"

```bash
$ cd workshop
$ ls
folder_01  folder_02
```

`-l` gives long output

```bash
$ ls -l
total 0
drwx------ 2 schmittu domainusers 0 Jun  4 21:06 folder_01
drwx------ 2 schmittu domainusers 0 Jun  4 21:06 folder_02
```

```bash
$ ls -l folder_01
total 16
-rwx------ 1 schmittu domainusers 6 Jun  4 21:06 hi.txt
-rwx------ 1 schmittu domainusers 6 Jun  4 21:06 ho.txt
```

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## Listing files (continued)

```bash
drwx------ 2 schmittu domainusers 0 Jun  4 21:06 folder_01
```

1. The `d` in the first column refers to "directory", for file you see a `-`.

2. The following 3 groups of 3 characters are file or folder permissions. More
   about this on the next slide.

3. The `2` is a so called link count.

Then the owner of the file and the group of the file are named.

The following `0` refers to the size and the timestamp describes the latest
change.

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## About file permissions

```bash
-rw-r--r-- 2 schmittu domainusers 0 Jun  8 21:04 instructions.txt
drwxrx---- 2 schmittu domainusers 0 Jun  4 21:06 folder_01
 ^^^^^^^^^
 FILE PERMISSIONS
```
This is how to interpret file permissions by positions:

- The first three characters refer to the owner of the file (here `schmittu`),
- The next three characters refer to the group the user belongs to (here `domainusers`),
- The last three characters refer to all other users.

And this are the meanings of the characters:

- `r`: allowed to read.
- `w`: allowed to write.
- `x`: allowed to run as a programm / allowed to `cd` if it is a folder.
- '-': not allowed.

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## About file permissions, continued.

```bash
-rw-r--r-- 2 schmittu domainusers 0 Jun  8 21:04 instructions.txt
drwxrx---- 2 schmittu domainusers 0 Jun  4 21:06 folder_01
 ^^^^^^^^^
 FILE PERMISSIONS
```
So in the example above:

- `instructions.txt` is a file which is readable by all users on the system and
can be written by the owner.

- `folder_01` is a directory. The owner and group members are allowed to `cd` to the folder
   and to list the content.

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## globbing

The character `*` refers to an arbitrary string (text) of length 0 or greater.

```bash
ls fol*1
hi.txt  ho.txt
```

`?` represents one single arbitrary character:

```bash
ls -l ?older_?2
total 8
-rwx------ 1 schmittu domainusers 40 Jun  4 21:06 today.txt
```

Both `*` and / or `?` can occur multiple times

```bash
ls -l */*.txt
-rwx------ 1 schmittu domainusers  6 Jun  4 21:06 folder_01/hi.txt
-rwx------ 1 schmittu domainusers  6 Jun  4 21:06 folder_01/ho.txt
-rwx------ 1 schmittu domainusers 40 Jun  4 21:06 folder_02/today.txt
```

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## Moving / renaming

The `mv` command allows to move and / or rename files and folders

```bash
$ mv folder_01/hi.txt .
$ ls -l
total 8
drwx------ 2 schmittu domainusers 0 Jun  4 21:18 folder_01
drwx------ 2 schmittu domainusers 0 Jun  4 21:06 folder_02
-rwx------ 1 schmittu domainusers 6 Jun  4 21:06 hi.txt
```

```bash
$ mv hi.txt greet.txt
$ ls -l
total 8
drwx------ 2 schmittu domainusers 0 Jun  4 21:18 folder_01
drwx------ 2 schmittu domainusers 0 Jun  4 21:06 folder_02
-rwx------ 1 schmittu domainusers 6 Jun  4 21:06 greet.txt
```

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## Copying / removing

```bash
$ cp greet.txt backup.txt
$ ls -l
total 8
drwx------ 2 schmittu domainusers 0 Jun  4 21:18 folder_01
drwx------ 2 schmittu domainusers 0 Jun  4 21:06 folder_02
-rwx------ 1 schmittu domainusers 6 Jun  4 21:06 backup.txt
-rwx------ 1 schmittu domainusers 6 Jun  4 21:06 greet.txt
```

```bash
$ rm greet.txt
$ ls -l
total 8
drwx------ 2 schmittu domainusers 0 Jun  4 21:18 folder_01
drwx------ 2 schmittu domainusers 0 Jun  4 21:06 folder_02
-rwx------ 1 schmittu domainusers 6 Jun  4 21:06 backup.txt
```

```bash
$ mv backup.txt greet.txt
$ ls -l
total 8
drwx------ 2 schmittu domainusers 0 Jun  4 21:18 folder_01
drwx------ 2 schmittu domainusers 0 Jun  4 21:06 folder_02
-rwx------ 1 schmittu domainusers 6 Jun  4 21:06 greet.txt
```

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## Redirecting output

The `>` can be used to redirect output to a file:

```bash
$ ls -l * > out.txt
$ ls -l
total 16
drwx------ 2 schmittu domainusers   0 Jun  4 21:18 folder_01
drwx------ 2 schmittu domainusers   0 Jun  4 21:06 folder_02
-rwx------ 1 schmittu domainusers   6 Jun  4 21:22 greet.txt
-rwx------ 1 schmittu domainusers 215 Jun  4 21:23 out.txt
```

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## Showing content of a file

```bash
$ cat out.txt
-rwx------ 1 schmittu domainusers 6 Jun  4 21:22 greet.txt

folder_01:
total 8
-rwx------ 1 schmittu domainusers 6 Jun  4 21:06 ho.txt

folder_02:
total 8
-rwx------ 1 schmittu domainusers 40 Jun  4 21:06 today.txt
```

---

## Writing to a file

```bash
$ echo hi
hi
```

`>>` appends to the file:

```bash
$ echo hi > new.txt
$ echo ho >> new.txt
$ cat new.txt
hi
ho
```

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- Show TAB completion and navigation with cursor keys!

- Show use of cursor keys

- Show use of nano text editor