Bash

📂 ls – List Directory Contents

Syntax:

ls [OPTIONS] [FILES...]

Options:

Option	Description
-l	Long listing format
-a	Show hidden files
-h	Human-readable file sizes
-R	Recursively list directories
-t	Sort by modification time
-r	Reverse sort order

Examples:

ls
ls -l
ls -la
ls -lh
ls -ltr

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📁 cd – Change Directory

Syntax:

cd [directory]

Examples:

cd            # Home directory
cd /etc       # Go to /etc
cd ..         # One level up
cd -          # Switch to previous dir

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📍 pwd – Print Working Directory

Syntax:

pwd

Description: Prints the full path of the current directory.

Example:

pwd
# Output: /home/user/Desktop

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🗨️ echo – Display Messages

Syntax:

echo [OPTIONS] [STRING...]

Options:

Option	Description
-n	Do not print newline
-e	Enable backslash escapes
-E	Disable escape interpretation (default)

Examples:

echo "Hello"
echo -n "Same line"
echo -e "Line1\nLine2\tTabbed"

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📄 cat – Concatenate and View Files

Syntax:

cat [OPTIONS] [FILES...]

Options:

Option	Description
-n	Number all lines
-b	Number only non-blank lines
-E	Show $ at end
-T	Show tabs as ^I

Examples:

cat file.txt
cat -n file.txt
cat file1.txt file2.txt > combined.txt

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📋 cp – Copy Files and Directories

Syntax:

cp [OPTIONS] SOURCE DEST

Options:

Option	Description
-r	Copy directories recursively
-u	Only copy if newer
-i	Prompt before overwrite
-v	Verbose output

Examples:

cp file.txt backup.txt
cp -r dir1/ dir2/
cp -uv config.sh /etc/

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🚚 mv – Move or Rename Files

Syntax:

mv [OPTIONS] SOURCE DEST

Options:

Option	Description
-i	Prompt before overwrite
-u	Move only if newer
-v	Verbose output

Examples:

mv old.txt new.txt
mv file.txt ~/Downloads/
mv -iv script.sh /usr/local/bin/

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❌ rm – Remove Files or Directories

Syntax:

rm [OPTIONS] FILE...

Options:

Option	Description
-r	Recursively delete dirs
-f	Force delete (no prompt)
-i	Ask before delete
-v	Show deleted files

Examples:

rm file.txt
rm -rf /tmp/test/
rm -iv backup.zip

⚠️ rm -rf can delete everything — use with extreme caution!

🕒 touch – Create or Update File Timestamp

Syntax:

touch [OPTIONS] FILE...

Options:

Option	Description
-c	Don’t create if missing
-a	Change access time
-m	Change modification time
-t	Use custom time: [[CC]YY]MMDDhhmm[.ss]

Examples:

touch newfile.txt
touch -c file.txt
touch -t 202507041200.00 data.log

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📦 mkdir – Create Directories

Syntax:

mkdir [OPTIONS] DIRECTORY...

Options:

Option	Description
-p	Create parent directories
-v	Show created directories

Examples:

mkdir mydir
mkdir -p parent/child/grandchild
mkdir -vp logs/errors/

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📘 man – Manual Page Viewer

Syntax:

man [COMMAND]

Description:
Shows the manual page for a command.

Examples:

man ls
man bash

Press q to exit.

🧩 alias – Create Command Shortcuts

Syntax:

alias name='command'

Examples:

alias ll='ls -l'
alias gs='git status'
alias rm='rm -i'
alias update='sudo apt update && sudo apt upgrade'

Remove alias:

unalias ll

💡 To make the alias permanent across terminal sessions, add it to your ~/.bashrc file:

echo "alias ll='ls -l'" >> ~/.bashrc
source ~/.bashrc  # Apply changes immediately

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