CLI

Command Line Review

BY Guanqiao Huang

Posted by HUANG on December 14, 2020

The command line is a text interface for the computer’s operating system. To access the command line, we use the terminal.
A filesystem organizes a computer’s files and directories into a tree structure. It starts with the root directory. Each parent directory can contain more child directories and files.

From the command line, you can navigate through files and folders on your computer:

pwd outputs the name of the current working directory.
ls lists all files and directories in the working directory.
cd switches you into the directory you specify.
mkdir creates a new directory in the working directory.
touch creates a new file inside the working directory.

You can use helper commands to make navigation easier:

clear clears the terminal
tab autocompletes the name of a file or directory
↑ and ↓ allow you to cycle through previous commands

MANIPULATION

Options modify the behavior of commands:

ls -a lists all contents of a directory, including hidden files and directories
ls -l lists all contents in long format
ls -t orders files and directories by the time they were last modified
Multiple options can be used together, like ls -alt

From the command line, you can also copy, move, and remove files and directories:

cp copies files
mv moves and renames files
rm removes files
rm -r removes directories Wildcards are useful for selecting groups of files and directories

REDIRECTION

Redirection reroutes standard input, standard output, and standard error.

The common redirection commands are:

> redirects standard output of a command to a file, overwriting previous content.
>> redirects standard output of a command to a file, appending new content to old content.
< redirects standard input to a command.
| redirects standard output of a command to another command.

A number of other commands are powerful when combined with redirection commands:

sort: sorts lines of text alphabetically.
uniq: filters duplicate, adjacent lines of text.
grep: searches for a text pattern and outputs it.
sed : searches for a text pattern, modifies it, and outputs it.

ENVIRONMENT

The environment refers to the preferences and settings of the current user.
The nano editor is a command line text editor used to configure the environment.
~/.bash_profile` is where environment settings are stored. You can edit this file with nano.

Environment variables are variables that can be used across commands and programs and hold information about the environment.

export VARIABLE="Value" sets and exports an environment variable.
USER is the name of the current user.
PS1 is the command prompt.
HOME is the home directory. It is usually not customized.
PATH returns a colon : separated list of file paths. It is customized in advanced cases.
env returns a list of environment variables. You can redirect the output, using grep to select the variable you want to see.

Additional Resources

Vim Cheat Sheet