Bash Scripting Basics

Shell (bash) Scripts

• Shell scripts are files containing shell commands.
• The first line starts with #! followed by the interpreter (e.g., #!/bin/sh).
• To run a script, grant execution permissions using chmod +x script_name.

Shell Script Examples (1)

• Create a file s1.sh.
• Add the shebang line (#!/bin/bash).
• Add commands like clear, CAR="Golf is the best", echo "CAR:", echo CAR, echo '$CAR:', echo $CAR.

Shell Script Examples (2)

• Create a file s2.sh.
• Add the shebang line (#!/bin/bash).
• Define an array CAR=(bmw audi toyota).
• Use array indexing like echo "CAR[0]=${CAR[0]}".
• Print array elements using echo "ALL - ${CAR[*]}", echo "Alternative ALL - ${CAR[@]}".

Shell Script Examples (3)

• Create a file s3.sh.
• Add the shebang line (#!/bin/bash).
• Use echo -n to display a prompt for user input.
• Use the read command to get user input.
• Store the user input in the REPLY variable.
• Display the input with echo "Your selected car - $REPLY".

Shell Script Examples (4)

• Create a file s4.sh.
• Add the shebang line (#!/bin/bash).
• Clear the terminal using clear.
• Use date to get the current date and format it using backticks (date).
• Store the date in the variable DATE. Print the date using echo "Today's date = $DATE".
• Get the number of users using who | wc -l
• Store the number of users in USERS variable.
• Display the number of users in the system. echo "Users in the system = $USERS".

Shell Script Examples (5)

• Create a file s5.sh.
• Add the shebang line (#!/bin/bash).
• Use arithmetic expansion with shell variables for calculations, like echo "2*2=$((2*$PERM ))" and echo "((2*3+5)-4)/2=$((((2*3+5)-4)/2 ))".

Shell Script Examples (6)

• Create a file s6.sh.
• Add the shebang line (#!/bin/bash).
• Use conditional statements (if, then, else, fi) to check whether a file exists.
• Use rm test 2>/dev/null to remove "test" file without error messages.
• Print echo "Deleted" if file deletion is successful.
• Otherwise print echo "Not deleted".

Explore the foundational concepts of bash scripting with this quiz. Learn about shebang lines, variables, and arrays, and how to execute scripts effectively. Test your knowledge with practical examples and commands used in creating shell scripts.