# Commands

## Manipulating files

Commands that can be used for reading and manipulating files

#### tail

`tail` by default reads the last 5 lines of the input file and then exits

```bash
Useful Flags    Function
-n *x*          Returns the last x lines of a file
-f              Follows the end of the file, so any new data will be printed out to the screen
```

#### head

`head` by default reads the first 5 lines of the input file and then exits

```bash
Useful Flags        Function
-n *x*              Returns the first x lines of a file
```

#### awk

`awk` is used to extract, layout and modify data using the command line (It is way more then this but its all I use it for)

#### sed

`sed` is the '**S**tream **ED**itor' you can use to to modify files via commands and scripts using patterns, an [example](examples/seddnszone.md) can be seen here

```bash
Useful Flags        Function
-i                  In-place, writes the changes to the file
-f                  Use a script file instead of reading the expression from STDIN
```

#### grep

`grep` is used to match text in a file, 

```bash
Useful Flags    Function
-o              Returns only the matched data (Useless without regex really)
-E              Allows extended regex to be used in the search, [regex info](/regex)
-P              Allows the use of Perl regex, this uses a different syntax to -E
-i              Makes the search case insensitive
-r              Searches files recursively (i.e if you have quite a few files and folders it will search through all of them)
-l              Returns the filename where the data was matched instead of the matched data
```

Some examples of grep usage can be found [here](/examples/grep)

#### lsof

`lsof` is a command that will show you what processes have specified file open currently you can see an example [here](/examples/lsof)

## Manipulating the standard input

These commands can be used to manipulate data in the standard input

#### rev