🐚 Shell Scripting One-Page Manual (Bash)

📌 Basics

Shebang (First Line)

#!/bin/bash

Tells the system to use Bash to run the script.

Run a Script

chmod +x script.sh     # Make executable
./script.sh            # Run

---

🔧 Variables

NAME="Alice"
echo "Hello, $NAME"

• No space around =
• Use $VAR to access

---

🧮 Conditionals

if [ "$AGE" -ge 18 ]; then
    echo "Adult"
else
    echo "Minor"
fi

Comparison operators:

• Strings: =, !=, -z, -n
• Numbers: -eq, -ne, -lt, -le, -gt, -ge

---

🔁 Loops

For Loop

for i in 1 2 3; do
    echo $i
done

While Loop

while [ "$x" -le 5 ]; do
    echo $x
    ((x++))
done

---

📦 Functions

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

• $1, $2, etc. are arguments
• return optional; use echo for output

---

📁 File Tests

if [ -f file.txt ]; then
    echo "It's a file"
fi

• -f: regular file
• -d: directory
• -e: exists
• -r, -w, -x: read/write/execute

---

📚 Useful Built-ins

Command	Purpose
read VAR	Read input
echo	Print text
cd, pwd	Change/print directory
exit	Exit script
source file	Run a script in current shell

---

📑 Tips

• Use set -e to exit on error
• Use #!/bin/bash -x for debugging
• Quote variables: "$VAR" to avoid word splitting
• Always check $? for last command status

---

🐚 Bash Shell Scripting Cheat Sheet

---

🔹 BASICS

#!/bin/bash         # Shebang
chmod +x script.sh  # Make script executable
./script.sh         # Run script

---

🔹 VARIABLES

NAME="Alice"
echo "Hello, $NAME"

• No spaces around =
• Use "$VAR" to prevent word splitting

---

🔹 CONDITIONALS

if [ "$A" -gt 10 ]; then
  echo "Greater"
elif [ "$A" -eq 10 ]; then
  echo "Equal"
else
  echo "Less"
fi

Operators:

Type	Operators
Strings	=, !=, -z, -n
Numbers	-eq, -ne, -lt, -le, -gt, -ge
Files	-f, -d, -e, -r, -w, -x

---

🔹 LOOPS

# For Loop
for i in 1 2 3; do echo $i; done

# While Loop
while [ $x -le 5 ]; do echo $x; ((x++)); done

---

🔹 FUNCTIONS

myfunc() {
  echo "Arg1 is $1"
}
myfunc "Hello"

---

🔹 INPUT & OUTPUT

read -p "Enter name: " NAME
echo "You typed: $NAME"

---

🔹 SPECIAL VARIABLES

Symbol	Description
$0	Script name
$1..$9	Arguments
$#	Number of arguments
$@	All arguments
$?	Exit status of last command
$$	PID of script

---

🔹 FILE TESTS

[ -f file.txt ] && echo "Regular file"
[ -d dir ] && echo "Directory"
[ -e path ] && echo "Exists"

---

🔹 DEBUGGING & SAFETY

set -e    # Exit on error
set -u    # Error on undefined variables
set -x    # Debug mode (prints commands)