tools

Basic Linux Commands

Note: In these, and all other examples in the cheatsheets, the $ prefix before a command indicates the use of a linux command line input. It is not part of the command - it is there to show you which lines are input, and which are output (lines without a $ prefix)

Check Current Working Directory

Where are you on this file system? Find out with pwd:

$ pwd
/var/www/html

Useful just after landing a shell or if you get lost.

Change Directory

The cd command changes directory:

$ pwd
/home/mac
$ cd /opt
$ pwd
/opt

Go to your home directory:

$ cd ~

Go back to the previous directory:

$ cd -

Go to the root of the filesystem:

$ cd /

List Files

List files in the current working directory:

$ ls

List all files, including hidden ones (preceded by a ., e.g. .env):

$ ls -a

Display extra information about files, including timestamps and file ownership:

$ ls -l

Combine the two:

$ ls -la

Switch User

The su command switches to another user on the machine. You must know their password.

This command will attempt to switch to the jane user:

$ su jane

If no username is provided, su will attempt to login as root:

$ su

Using the - flag simulates a real login - you will often see su - in writeups as shorthand for su root:

$ su -

However this command is effectively the same as the one above, apart from a few small differences like the clearing of environment variables.

grep

grep is an incredibly useful command that allows searching the contents of files and the outputs of terminal commands.

Grepping a File

$ grep [SEARCH_TERM] /path/to/file

or, using pipe (|):

$ cat /path/to/file | grep [SEARCH_TERM]

Grepping Terminal Output

You can use the pipe operator to run grep on the output of any command. A common use case is searching the output of a directory.

$ ls -la | grep [SEARCH_TERM]

awk

awk can be used for manipulating structured text and extracting specific fields. Think of it as a way of selecting a specific column from a load of structured data.

For example, a list of employee names:

$ cat employees
John Doe
Jane Doe

awk could be used to extract the first names of these employees:

$ cat employees | awk '{print $1}'

Where $x represents the xth column (1-indexed).

You can specify a different ‘field separator’ with the -F flag:

$ cat employees
John:Doe
Jane:Doe
$ cat employees | awk -F ':' '{print $1}'
John
Jane