Bash Commands

Navigation

Command	Description
cd [directory]	Change the current working directory to [directory]
pwd	Print the current working directory
ls	List the contents of the current directory
ls [directory]	List the contents of [directory]

Manipulating Files and Directories

Command	Description
mkdir [directory]	Create a new directory named [directory]
touch [filename]	Create a new file named [filename]
cp [source] [destination]	Copy [source] to [destination]
mv [source] [destination]	Move [source] to [destination]
rm [file]	Remove [file]
rm -r [directory]	Remove [directory] and its contents

Input and Output

Command	Description
echo [message]	Print [message] to the console
cat [file]	Print the contents of [file] to the console
head [file]	Print the first 10 lines of [file] to the console
tail [file]	Print the last 10 lines of [file] to the console

Searching

Command	Description
grep [pattern] [file]	Search [file] for lines containing [pattern]
grep -r [pattern] [directory]	Recursively search [directory] for files containing [pattern]

Permissions

Command	Description
chmod [mode] [file]	Change the permissions of [file] to [mode]
chown [user] [file]	Change the owner of [file] to [user]
chgrp [group] [file]	Change the group of [file] to [group]

System Information

Command	Description
whoami	Print the current user's username
hostname	Print the name of the current host
uptime	Print the system uptime

Process Management

Command	Description
ps	List the currently running processes
ps aux	List all running processes and their details
kill [process_id]	Send a signal to stop the process with [process_id]
killall [process_name]	Send a signal to stop all processes with the name [process_name]

Networking

Command	Description
ping [host]	Test the connectivity to [host] by sending ICMP echo request packets
traceroute [host]	Show the path taken by packets to reach [host]
wget [url]	Download a file from [url]
curl [url]	Transfer data from or to a server using various protocols including HTTP, FTP, etc.

System Maintenance

Command	Description
df	Show the amount of free disk space on each mounted filesystem
du [directory]	Show the disk usage of the files and directories within [directory]
top	Display the system's processes in real time
history	Show a list of commands previously executed by the user

User Management

Command	Description
useradd [username]	Create a new user account with the username [username]
userdel [username]	Delete the user account with the username [username]
passwd [username]	Change the password for the user account with the username [username]
su [username]	Switch to the user account with the username [username]

Miscellaneous

Command	Description
date	Display the current date and time
cal	Display a calendar for the current month
clear	Clear the terminal screen
exit	Exit the current terminal session

These are just some of the most commonly used Bash commands, but there are many more. It's worth noting that most of these commands have additional options and arguments that can be used to customize their behavior, and you can find more information about them in the Bash manual or by using the man command followed by the name of the command.

Piping in Bash

Piping is a powerful feature in Bash that allows you to take the output of one command and use it as the input for another command. This allows you to chain together multiple commands to perform more complex operations.

Syntax

To pipe the output of one command to the input of another command, you use the | character. For example:

command1 | command2

In this syntax, command1 produces output, which is then passed as input to command2.

Examples

Here are some examples of piping in Bash:

Example 1: Counting files

To count the number of files in the current directory, you could use the following command:

ls | wc -l

In this command, ls lists all the files in the current directory, and the output is piped to the wc command, which counts the number of lines in the input.

Example 2: Searching for files

To search for all files in the current directory that contain the word "hello", you could use the following command:

ls | grep hello

In this command, the output of ls is piped to the grep command, which searches for the word "hello" in the input and returns any lines that contain the word "hello".

Example 3: Chaining commands

You can chain together any number of commands using piping. For example, you could search for all files in the current directory that contain the word "hello", count the number of lines that contain the word "hello", and then sort the output by the number of lines using the sort command like this:

ls | grep hello | wc -l | sort

In this command, the output of ls is piped to the grep command, which searches for the word "hello" in the input. The output of grep is then piped to the wc command, which counts the number of lines that contain the word "hello". Finally, the output of wc is piped to the sort command, which sorts the output by the number of lines.

By mastering piping, you can become much more efficient and productive on the command line.

Vim

Vim is a powerful text editor that is included with most Unix-based operating systems, including Linux and macOS. It is designed to be used in a terminal window and provides a wide range of features for editing text, including syntax highlighting, code folding, and macro recording.

Basic Usage

To open a file in Vim, you simply type the vim command followed by the name of the file you want to edit. For example:

vim example.txt

Once the file is open, you can use a wide range of commands to edit the text. Some basic commands include:

• i to enter insert mode, where you can type new text
• Esc to exit insert mode and return to command mode
• :w to save the changes you've made to the file
• :q to quit Vim
• :wq to save the changes and quit Vim

Advanced Features

Vim has many advanced features that can help you edit text more efficiently. For example:

• Macros: You can record a series of keystrokes as a macro and then play it back to repeat the same series of commands on multiple lines of text.
• Plugins: Vim has a wide range of plugins that you can use to add new features to the editor, such as code completion, file browsing, and syntax checking.
• Customization: Vim is highly customizable, and you can configure it to work the way you want by editing the vimrc file.

Emacs

Emacs is another powerful text editor that is widely used in the Unix/Linux world. Like Vim, it is designed to be used in a terminal window, but it also has a graphical user interface (GUI) version that can be run on most operating systems.

Basic Usage

To open a file in Emacs, you simply type the emacs command followed by the name of the file you want to edit. For example:

emacs example.txt

Once the file is open, you can use a wide range of commands to edit the text. Some basic commands include:

• Ctrl + x, Ctrl + s to save the changes you've made to the file
• Ctrl + x, Ctrl + c to quit Emacs
• Ctrl + g to cancel the current command or operation
• Ctrl + x, Ctrl + f to open a new file for editing
• Ctrl + x, Ctrl + b to switch between open files

Advanced Features

Emacs has many advanced features that can help you edit text more efficiently. For example:

• Macros: You can record a series of keystrokes as a macro and then play it back to repeat the same series of commands on multiple lines of text.
• Modes: Emacs has modes for editing specific types of files, such as programming languages or markup languages. These modes provide syntax highlighting and other features specific to the language or format.
• Plugins: Emacs has a wide range of plugins that you can use to add new features to the editor, such as code completion, version control integration, and file browsing.
• Customization: Like Vim, Emacs is highly customizable, and you can configure it to work the way you want by editing the .emacs file.

The >> operator

The >> operator is a Bash command that appends the output of a command to the end of a file. Here's an example:

echo "Hello, world!" >> example.txt

In this command, the echo command outputs the text "Hello, world!" to the terminal window, and the >> operator appends the output to the end of the file example.txt. If the file doesn't exist, the >> operator creates it.

You can use the >> operator with any command that produces output. For example, you could use it with the ls command to append a list of files in the current directory to a file:

ls >> filelist.txt

In this command, the output of ls (a list of files in the current directory) is appended to the end of the file filelist.txt.

Regular Expressions (Regex) 101

Regular expressions, also known as regex, are a powerful operator for working with text. A regular expression is a pattern of characters that describes a set of strings. For example, the regular expression hello matches the strings "hello", "Hello", and "heLLo".

Basic Syntax

Regular expressions are composed of characters that match specific patterns of text. Here are some examples of basic syntax:

• .: Matches any single character
• [ ]: Matches any one of the characters in the brackets
• [^ ]: Matches any character not in the brackets
• *: Matches zero or more occurrences of the previous character
• +: Matches one or more occurrences of the previous character
• ?: Matches zero or one occurrence of the previous character
• |: Matches either the expression on the left or the expression on the right

For example, the regular expression b[aeiou]t matches the strings "bat", "bet", "bit", "bot", and "but".

Advanced Syntax

Regular expressions can also include more advanced syntax to match more complex patterns. Here are some examples:

• ^: Matches the beginning of a line
• $: Matches the end of a line
• () and |: Matches groups of characters and allows you to specify alternatives within the group. For example, the regular expression (cat|dog) matches the strings "cat" and "dog".
• \: Escapes special characters so they are treated as literal characters. For example, the regular expression \. matches a period.

Practical Uses

Regular expressions are used in many different programming languages and operators, including Bash, Python, Perl, and more. Some common uses for regular expressions include:

• Validating input: Regular expressions can be used to ensure that user input matches a specific pattern. For example, you could use a regular expression to validate an email address or a phone number.
• Searching and replacing: Regular expressions can be used to search for specific patterns of text and replace them with other text. For example, you could use a regular expression to replace all occurrences of a word in a document.
• Extracting information: Regular expressions can be used to extract specific pieces of information from a larger text. For example, you could use a regular expression to extract all of the email addresses from a file.

Overall, regular expressions are a powerful operator for working with text, and they can be used to solve many different problems.

CLI Hotkeys, Tips, and Tricks

The Bash command-line interface (CLI) is a powerful operator for working with files, directories, and other aspects of your operating system. Here are some hotkeys, tips, and tricks to help you get the most out of Bash.

Hotkeys

Hotkeys are keyboard shortcuts that allow you to perform certain actions in Bash more quickly. Here are some commonly used hotkeys:

• Ctrl + c: Stop the current command or process
• Ctrl + z: Suspend the current command or process
• Ctrl + d: Exit the current shell or terminal
• Ctrl + a: Move the cursor to the beginning of the line
• Ctrl + e: Move the cursor to the end of the line
• Ctrl + u: Delete the text from the cursor to the beginning of the line
• Ctrl + k: Delete the text from the cursor to the end of the line
• Ctrl + r: Search the command history

Tips

Here are some tips for using Bash more effectively:

• Use the man command to access the manual pages for other commands. For example, man ls will display the manual page for the ls command.
• Use the tab key to autocomplete commands and filenames. For example, if you type ls /ho and then press tab, Bash will autocomplete /ho to /home.
• Use the history command to view a list of your previous commands. You can then use !n to run a specific command from your history, where n is the number of the command in the list.
• Use the && operator to run multiple commands in sequence. For example, ls && pwd will run the ls command and then the pwd command.
• Use the > and >> operators to redirect output to a file. For example, ls > file.txt will write the output of the ls command to file.txt.

Tricks

Here are some tricks that can help you be more productive with Bash:

• Use aliases to create shortcuts for frequently used commands. For example, you could create an alias for ls -l as ll.
• Use wildcards to perform operations on multiple files at once. For example, rm *.txt will delete all files with a .txt extension in the current directory.
• Use grep to search for specific text within files. For example, grep "error" file.txt will display all lines in file.txt that contain the word "error".
• Use sed to perform search-and-replace operations on files. For example, sed "s/old/new/g" file.txt will replace all occurrences of "old" with "new" in file.txt.
• Use awk to perform more complex operations on files. For example, awk '{print $1}' file.txt will display the first column of data in file.txt.

By using these hotkeys, tips, and tricks, you can become more efficient and effective at using Bash to manage your files and directories.

Reserved symbols in Bash:

• .: Represents the current directory. For example, ./script.sh runs the script.sh script in the current directory.
• ..: Represents the parent directory. For example, ../file.txt refers to a file named file.txt in the parent directory of the current directory.
• ~: Represents the home directory of the current user. For example, ~/file.txt refers to a file named file.txt in the home directory of the current user.
• /: Represents the root directory, the top-level directory in the file system hierarchy. For example, /etc/passwd refers to the passwd file in the etc directory at the root of the file system.

These symbols are used in Bash commands to navigate the file system and perform operations on files and directories. Understanding how to use them is crucial for effective file management in Bash.

Here are some examples of how to use these symbols in Bash:

• cd ..: Changes the current working directory to the parent directory of the current directory.
• ls ~/: Lists the contents of the home directory of the current user.
• cp file.txt /tmp/: Copies the file file.txt to the /tmp directory.
• rm -r /var/log/: Removes the entire /var/log directory and its contents.

Remember to use these symbols carefully, as they can be powerful and potentially dangerous when used incorrectly.