💻 Shell Scripting Notes

🔹 Basic Syntax

• #!/bin/bash — Shebang to define the shell interpreter
• # — Single-line comment
• echo "Hello" — Print output
• read name — Accept user input
• $(command) or \`command\` — Command substitution

🔄 Conditionals & Loops

• if [ $a -eq $b ]; then ... fi — Basic if condition
• elif and else — Additional condition checks
• while [ condition ]; do ... done — While loop
• for i in {1..5}; do ... done — For loop
• case $var in ...) esac — Case/switch logic

🧠 Variables & Parameters

• var=value — Assign variable (no space before/after =)
• $var — Access variable
• $1, $2, ... — Script arguments
• $# — Number of arguments
• $? — Exit status of last command

📁 File & Directory Handling

• [ -f file.txt ] — Check if file exists
• [ -d dir ] — Check if directory exists
• touch, mkdir, rm, mv — File operations
• cat, head, tail, grep — Read/search files

🔧 Practical Example

#!/bin/bash
echo "Enter a filename:"
read fname

if [ -f "$fname" ]; then
    echo "Contents of $fname:"
    cat "$fname"
else
    echo "$fname does not exist!"
fi