> For the complete documentation index, see [llms.txt](https://lauradang.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://lauradang.gitbook.io/notes/c++/cs_246/lecture-1.md).

# Lecture 1

## Linux Shell

Shell: Interface to the OS

* gets OS to do stuff - run programs, manage files
* graphical shell (Windows, Mac OS, Ubuntu)
* command line (type commands - terminal)

In this course, we use Bash.

```bash
# type this to ensure you are in bash
$ echo $0
>> -bash
```

## Files, Input/Output

#### `$ cat`

* Displays contents of root directory
* First slash denotes root directory (top of directory hierarchy)

```bash
$ cat /path/to/file
```

What if I just run :

* Copies output
* Is this useful?
  * Can capture output and put in a file -`cat > output.txt`

```bash
# Example
$ cat
hello
>> hello
hi
>> hi
```

Stopping cat from running: `Ctrl+D`

## Text in Linux

In linux, every line in valid txt file must end with a newline character.

* Marmoset checks that last line ends in 
* When printing output, should end in 

## Terminating program

* For infinite loop or crash, to terminate program: `Ctrl+C`

### `$ ls`

* Displays file in current dir

### `$ ls -a`

* Displays hidden files + files in current dir

### `$ pwd`

* prints the current dir
* stands for present working directory

## Redirecting Output

* output redirection symbol: `>`
* what would be printed to output, send to file

```bash
# Example:
$ cat args > file
```

## Redirecting Input

* input redirection symbol: `<`

```bash
# Example:
$ cat < inputfile
```

* reads intput from file instead of keyboard
* in the case of `$ cat`, the output is the same

## Difference in Behaviour

* **$ cat /file** -> pass "file" as an argument to cat which opens the file and prints it
* **$ cat < file** -> the **shell** opens the file and passes its content in place of keyboard input

## `$ wc`

* line count, word count, character count

## Asterisk in Linux (\*)

* \*.txt is a globbing pattern
* asterisk means match anything
* when shell sees globbing pattern, the shell expands globbing pattern to match non-hidden files
* More globbing patterns on reference sheet
* Many commands can accept arguments or input with the exception of `$ echo`

```bash
# Example:
## Copies input.txt into output.txt
$ cat < input.txt > output.txt
```

```bash
# Example:
## Prints output preceeded by line numbers
$ cat -n < input.txt > output.txt
```