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conditions, loops, functions, error handling, IOs, arrays, strings, debug

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Shell Scripting Tips and Guidelines

1. Basic Script Structure

#!/bin/bash

# This is a comment
echo "Hello, World!"

2. Variables

# Assigning a variable
MY_VAR="Hello"

# Accessing a variable
echo $MY_VAR

# Using variables in strings
echo "The value of MY_VAR is: ${MY_VAR}"

3. Conditional Statements

# If-else statement
if [ "$MY_VAR" == "Hello" ]; then
    echo "Greeting is Hello"
else
    echo "Greeting is not Hello"
fi

# Case statement
case $1 in
    start)
        echo "Starting";;
    stop)
        echo "Stopping";;
    *)
        echo "Usage: $0 {start|stop}"
        exit 1
esac

4. Loops

# For loop
for i in {1..5}; do
    echo "Looping ... number $i"
done

# While loop
COUNTER=1
while [ $COUNTER -le 5 ]; do
    echo "Count: $COUNTER"
    COUNTER=$((COUNTER + 1))
done

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5. Functions

my_function() {
    echo "This is a function"
}

# Calling a function
my_function

6. Error Handling

# Exit script on error
set -e

# Function to handle errors
error_exit() {
    echo "$1" 1>&2
    exit 1
}
# Example usage
cp /nonexistentfile /tmp || error_exit "File copy failed!"

7. Input and Output

# Reading input from the user
read -p "Enter your name: " NAME
echo "Hello, $NAME!"

# Redirecting output to a file
echo "This is a log message" >> mylogfile.log
# Redirecting error output
ls /nonexistent 2>> errors.log

8. Using Arrays

# Declaring an array
MY_ARRAY=("one" "two" "three")

# Accessing array elements
echo ${MY_ARRAY[0]}
echo ${MY_ARRAY[@]}
# Adding elements to an array
MY_ARRAY+=("four")
# Looping through an array
for element in "${MY_ARRAY[@]}"; do
    echo $element
done

9. String Manipulation

# String length
MY_STRING="Hello, World!"
echo ${#MY_STRING}

# Substring
echo ${MY_STRING:7:5}
# Replacing a substring
echo ${MY_STRING/World/Bash}

10. Debugging Scripts

# Enabling debugging mode
set -x

# Disabling debugging mode
set +x

Best Practices

1. Use comments to explain your code.
2. Follow naming conventions for variables and functions.
3. Check for errors after running commands.
4. Use functions to organize and reuse code.
5. Test your scripts in different environments.
6. Use version control (e.g., git) to manage your script libraries.
7. Avoid hardcoding values; use variables and configuration files instead.
8. Handle user input carefully to avoid injection attacks.