User Interaction and Real World Bash

User Interaction and Real World Bash

user-interaction.pdf

3. Options

while getopts u:p: option; do
        case ${option} in
                u) user=$OPTARG;;
                p) pass=$OPTARG;;
        esac
done

echo "user:$user / pass: $pass"

In our script, we can use the getopts keyword. We specify an opt string (option string) that defines the search criteria.

Here, we utilize u:p:. This means the script will have -u and -p options. A colon after each option indicates that the script expects an argument for each.

Within the loop, we assign each option to the variable option and utilize it in a case statement.

The OPTARG variable holds the argument value for each option.

Then, we finish our script with an echo statement, and save.

while getopts :u:p:ab option; do
	case $option in
		u) user=$OPTARG;;
		p) pass=$OPTARG;;
		a) echo "got the A flag";;
		b) echo "got the B flag";;
		?) echo "I don't know what $OPTARG is!";;
	esac
done

echo "user:$user / pass: $pass"

Adding a question mark ? will capture these unknown options in the case statement.

5.Input During Execution

#!/bin/bash

echo "What is your name?"
read name

echo "What is your password?"
read -s pass

read -p "What's your favorite animal? " animal

echo "Name: $name, Password: $pass, Fave Animal: $animal"

echo "Which animal"
select animal in "cat" "dog" "bird" "fish"

do
    echo "You selected $animal!"
    break
done

6. Responding

**Using the -i option with the read command allows us to suggest a response for the user. If the user presses return without entering a response, the suggested response will be used by default.

#!/usr/bin/env bash

read -ep "What is your pet's name? " -i "Pabu" petname

echo $petname

We can use a regular expression to check whether:

  • the input $zipcode

  • matches a 5-digit pattern {5}

  • containing digits [0-9]

When the condition is true, the loop stops and the program carries on.

#!/usr/bin/env bash

read -p "Please enter a 5-digit zip code: [nnnnn]" zipcode

until [[ $zipcode =~ [0-9]{5} ]]; do
    read -p "Still waiting on that zip code! [nnnnn] " zipcode
done

echo "Your zip code is $zipcode

7. Discovery 1

**1. Use the read command to request user input and return only after reading exactly 55 characters

Solution: The -N numOfChar returns only after reading exactly numOfChar characters, unless EOF is encountered or read times out.

read -N 5

The -n option allows us to define a character limit for a response.

read -n 20 -p "What is your favorite show?" faveShow

The -t option allows us to limit the amount of time taken to input text.

read -t 10 -p "What is the capital of Alaska?"

In Bash scripting, set -x is a command that enables the debugging mode, where the shell will print each command before it's executed. This is useful for understanding the flow of a script and debugging any issues.

Here's a simple example to demonstrate how set -x works:

bashCopy code
#!/bin/bash

# Enable debugging
set -x

# Sample script
echo "Starting the script"
name="John"
age=30
echo "My name is $name, and I'm $age years old."
echo "End of the script"

# Disable debugging
set +x
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