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Catalog / Linux/Bash Terminal Essentials

Linux/Bash Terminal Essentials

A handy cheat sheet for navigating and manipulating the Linux/Bash terminal environment, covering essential commands, shortcuts, and scripting tips.

Basic Navigation & File Management

Navigation Commands

pwd

Print working directory (current directory).

cd <directory>

Change directory. Use cd .. to go up one level.

ls

List files and directories in the current directory.

ls -l

List files with detailed information (permissions, size, modification date, etc.).

ls -a

List all files, including hidden files (files starting with .).

ls -t

List files sorted by modification time (newest first).

File Operations

mkdir <directory>

Create a new directory.

touch <file>

Create an empty file or update the modification timestamp of an existing file.

cp <source> <destination>

Copy a file or directory. Use cp -r for recursive copying of directories.

mv <source> <destination>

Move or rename a file or directory.

rm <file>

Remove a file. Warning: This is permanent! Use rm -r for directories, and rm -rf to force removal.

rmdir <directory>

Remove an empty directory. Use rm -r <directory> to remove non-empty directories.

File Content Viewing

cat <file>

Display the entire content of a file.

less <file>

View file content page by page. Use q to quit.

head <file>

Display the first few lines of a file (default 10 lines).

tail <file>

Display the last few lines of a file (default 10 lines).

tail -f <file>

Display the last few lines and follow the file as it grows. Useful for log files.

wc <file>

Word count - displays number of lines, words, and characters in a file.

Searching & Text Manipulation

Searching

grep <pattern> <file>

Search for a pattern within a file. Use grep -i for case-insensitive search.

grep -r <pattern> <directory>

Recursively search for a pattern within all files in a directory.

find <directory> -name <filename>

Find files by name within a directory.

find <directory> -type f

Find all files within a directory.

find <directory> -type d

Find all directories within a directory.

locate <filename>

Find files by name using a pre-built database. Requires updatedb to update the database.

Text Manipulation

sed 's/<old>/<new>/g' <file>

Replace all occurrences of <old> with <new> in a file using stream editor.

awk '{print $1}' <file>

Print the first column of each line in a file using AWK.

sort <file>

Sort the lines of a file.

uniq <file>

Remove duplicate lines from a file (usually used with sort).

cut -d '<delimiter>' -f <field> `

Cut out specific fields from a file based on a delimiter.

tr '[:lower:]' '[:upper:]' <file>

Convert all lowercase characters to uppercase in a file.

Piping and Redirection

|

Pipe the output of one command to the input of another.

Example: ls -l | grep .txt (list files and filter for .txt files)

>

Redirect the output of a command to a file, overwriting the file if it exists.

Example: ls > files.txt

>>

Append the output of a command to a file.

Example: echo 'New entry' >> logfile.txt

2>

Redirect standard error to a file.

Example: command 2> error.log

&>

Redirect both standard output and standard error to a file.

Example: command &> output.log

<

Redirect the content of a file to the input of a command.

Example: wc -l < file.txt

System Information & Process Management

System Information

uname -a

Display kernel information.

hostname

Display the system’s hostname.

df -h

Display disk space usage in a human-readable format.

du -sh <directory>

Display the disk usage of a directory in a human-readable format.

free -m

Display memory usage in megabytes.

uptime

Show how long the system has been running.

Process Management

ps aux

Display all running processes.

top

Display a dynamic real-time view of running processes.

kill <PID>

Terminate a process with the given PID (Process ID).

kill -9 <PID>

Forcefully terminate a process (use with caution).

bg

Put a stopped process in the background.

fg

Bring a background process to the foreground.

User Management

whoami

Display the current username.

id

Display user and group IDs.

passwd

Change the password for the current user.

sudo <command>

Execute a command with superuser privileges.

su <username>

Switch to another user.

groups

Display the groups the current user belongs to.

Bash Scripting Basics

Script Structure

All bash scripts should start with a shebang line, which tells the system which interpreter to use:

#!/bin/bash

Comments are denoted by #:

# This is a comment

Variables

Setting a variable:

variable_name="value" (no spaces around =)

Example:
NAME="John Doe"

Accessing a variable:

$variable_name or ${variable_name}

Example:
echo "Hello, $NAME"

Environment Variables:

Variables that are available system-wide (e.g., PATH, HOME). Access them the same way as regular variables.

Read-only variables:

readonly variable_name

Conditional Statements

if statement:

 
if [ condition ]; then
  commands
elif [ condition ]; then
  commands
else
  commands
fi

case statement:

 
case variable in
  pattern1)
    commands
    ;;
  pattern2)
    commands
    ;;
  *)
    commands # Default
    ;;
esac

Looping

for loop:

 
for variable in item1 item2 ...;
do
  commands
done

Example:
for i in {1..5}; do echo $i; done

while loop:

 
while [ condition ]; do
  commands
done

until loop:

 
until [ condition ]; do
  commands
done

Functions

Defining a function:

 
function_name () {
  commands
}

Or:

function function_name {
  commands
}

Calling a function:

function_name

Example:

greet () {
  echo "Hello, $1"
}

greet John

Returning a value:

Use return to return an exit status (0-255). Use echo to output a string value.
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