/Shell_Scripts

Primary LanguageShell

Shell Scripts

Enable Permission

chmod u+x script.sh

./script.sh

Sum two numbers in a single line

read -p "a:" a; read -p "b:" b; echo $((a + b))

Explanation:

  1. Reading input:
    • read -p "a:" a: Prompts the user to input a value for variable a. The -p option allows you to specify a prompt string ("a:") that is displayed to the user.
    • read -p "b:" b: Prompts the user to input a value for variable b. The -p option specifies the prompt string ("b:") that is displayed to the user.
  2. Performing arithmetic and printing the result:
    • echo $((a + b)): Performs the arithmetic operation of adding the values of a and b, and then prints the result. The $((...)) syntax is used for arithmetic expansion in the shell, which allows for performing calculations.

Math operation in a single line

read -p "a:" a; read -p "b:" b; read -p "o:" o; echo `expr $a $o $b`

Explanation:

  1. Reading input: (Refer to the explanation above)
    • read -p "a:" a
    • read -p "b:" b
    • read -p "o:" o: Prompts the user to input a value for variable o, which is expected to be a mathematical operator (e.g., +, -, *, /). The -p option specifies the prompt string ("o:") that is displayed to the user.
  2. Performing arithmetic and printing the result:
    • echo \expr $a $o $b`: Performs the arithmetic operation specified by the operator oon the values ofaandb, and then prints the result. The backticks `` ...`` are used for command substitution, where the expression inside the backticks is executed, and its output is returned. Theexprcommand evaluates the expression$a $o $b`.

Improved and safer version using bc

To handle floating-point arithmetic and avoid issues with certain operators, we can use bc (a command-line calculator):

read -p "a:" a; read -p "b:" b; read -p "o:" o; echo "$a $o $b" | bc

Explanation:

  1. Reading input: (Refer to the explanation above)
    • read -p "a:" a
    • read -p "b:" b
    • read -p "o:" o
  2. Performing arithmetic and printing the result:
    • echo "$a $o $b" | bc: Constructs the arithmetic expression and pipes it to bc for evaluation. This method handles floating-point numbers and more complex arithmetic operations.

One line loop

for val in {1..5}; do echo $val; done

Notes

# Reads input and sets it in variable 'a'
read -p "input number: " a

# Checks if both 'a' and 'b' are set
if [ -n "$a" -a -n "$b" ]; then
  echo "Both 'a' and 'b' are set."
fi

# Checks if either 'a' or 'b' is set
if [ -n "$a" -o -n "$b" ]; then
  echo "Either 'a' or 'b' is set."
fi

# Checks if 'a' is empty
if [ -z "$a" ]; then
  echo "'a' is empty."
fi

# Checks if the number of arguments is not equal to 2
if [ $# -ne 2 ]; then
  echo "The number of arguments is not equal to 2."
fi
# The symbol $# is the number of arguments
# The symbol -ne stands for "not equal"

# Evaluates expression
echo $(expr $a $operand $b)

# Reads two inputs and evaluates their sum
read -r x
read -r z
echo $(expr $x + $z)