Working with Parameters in a Shell Script (.sh)

Working with Parameters in a Shell Script (`.sh`)

In a bash script, you can handle parameters passed from the command line. Below are the main parameters and how to use them in your script:

1. Accessing Parameters

Parameters are accessible using positional variables inside the script:

$0: The script’s name.
$1, $2, …, $N: The values of the passed arguments.
$#: The number of arguments provided.
$@: All arguments as a list (each argument is treated as a separate string).
$*: All arguments as a single string.
$?: The return code of the last command.
$$: The process ID (PID) of the running script.
$_: The last argument of the previous command.

Basic Script Example with Parameters

#!/bin/bash

echo "Script name: $0"
echo "First argument: $1"
echo "Second argument: $2"
echo "Number of arguments: $#"

# Checking if an argument was provided
if [ $# -lt 1 ]; then
  echo "No argument was provided."
  exit 1
fi

# Iterating over all arguments
for arg in "$@"; do
  echo "Argument: $arg"
done

2. Using Flags with Arguments

For more sophisticated scripts, you can add flags like -h for help or -f for specifying a file:

#!/bin/bash

while getopts ":f:h" option; do
  case $option in
    f) # Parameter -f is passed
      file=$OPTARG
      echo "File: $file"
      ;;
    h) # Displays help
      echo "Usage: $0 -f [file] -h [help]"
      exit 0
      ;;
    \?) # Invalid flag
      echo "Invalid option: -$OPTARG"
      exit 1
      ;;
  esac
done

3. Complete Example: Processing Arguments and Flags

Here’s an example script that accepts options and parameters and validates input:

#!/bin/bash

function show_help {
  echo "Usage: $0 -n [name] -a [age]"
  exit 1
}

# Check if any arguments were passed
if [ $# -eq 0 ]; then
  show_help
fi

while getopts "n:a:h" opt; do
  case $opt in
    n)
      name=$OPTARG
      ;;
    a)
      age=$OPTARG
      ;;
    h)
      show_help
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      show_help
      ;;
    🙂
      echo "Option -$OPTARG requires an argument." >&2
      show_help
      ;;
  esac
done

# Validate input
if [ -z "$name" ] || [ -z "$age" ]; then
  show_help
fi

echo "Name: $name"
echo "Age: $age"

4. Making the Script Executable

After writing the script, you need to make it executable using the chmod command. Here’s how to do it:

chmod +x your_script.sh

This command grants execution permissions to the script. You can then run the script using:

./your_script.sh -n "John" -a 25

Code Section

#!/bin/bash

# Basic script with parameters
echo "Script name: $0"
echo "First argument: $1"
echo "Second argument: $2"
echo "Number of arguments: $#"

if [ $# -lt 1 ]; then
  echo "No argument was provided."
  exit 1
fi

for arg in "$@"; do
  echo "Argument: $arg"
done

#!/bin/bash

# Script with flags and argument processing
while getopts ":f:h" option; do
  case $option in
    f)
      file=$OPTARG
      echo "File: $file"
      ;;
    h)
      echo "Usage: $0 -f [file] -h [help]"
      exit 0
      ;;
    \?)
      echo "Invalid option: -$OPTARG"
      exit 1
      ;;
  esac
done

#!/bin/bash

# Complete script example with input validation
function show_help {
  echo "Usage: $0 -n [name] -a [age]"
  exit 1
}

if [ $# -eq 0 ]; then
  show_help
fi

while getopts "n:a:h" opt; do
  case $opt in
    n)
      name=$OPTARG
      ;;
    a)
      age=$OPTARG
      ;;
    h)
      show_help
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      show_help
      ;;
    🙂
      echo "Option -$OPTARG requires an argument." >&2
      show_help
      ;;
  esac
done

if [ -z "$name" ] || [ -z "$age" ]; then
  show_help
fi

echo "Name: $name"
echo "Age: $age"

# Making the script executable
chmod +x your_script.sh

edvaldo b. guimarães filho

Working with Parameters in a Shell Script (.sh)

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