Reading User Input

Interactive scripts need to gather input from users during execution. The read command is your primary tool for this.

The read Command

Basic usage of read:

#!/bin/bash
echo "What is your name?"
read NAME
echo "Hello, $NAME!"

When executed, the script pauses at read and waits for user input.

Read with Prompt

Use -p to display a prompt on the same line:

#!/bin/bash
read -p "Enter your name: " NAME
echo "Hello, $NAME!"

This is cleaner than separate echo and read commands.

Read Options

The read command has many useful options:

Option	Description
-p "prompt"	Display prompt before reading
-s	Silent mode (hide input, for passwords)
-n N	Read only N characters
-t N	Timeout after N seconds
-r	Raw mode (don't interpret backslashes)
-a array	Read into an array
-d 'char'	Use character as delimiter instead of newline

Silent Input for Passwords

Hide sensitive input with -s:

#!/bin/bash
read -sp "Enter password: " PASSWORD
echo    # Add newline after hidden input
echo "Password received (${#PASSWORD} characters)"

Note: The -s flag hides what the user types.

Reading with Timeout

Don't wait forever for input:

#!/bin/bash
read -t 5 -p "Quick! Enter something (5 seconds): " ANSWER

if [ -z "$ANSWER" ]; then
    echo "Too slow!"
else
    echo "You entered: $ANSWER"
fi

Reading Limited Characters

Read exactly N characters:

#!/bin/bash
read -n 1 -p "Press any key to continue... "
echo    # Newline

read -n 3 -p "Enter 3-letter code: " CODE
echo
echo "Code: $CODE"

Reading Multiple Variables

Read multiple values into multiple variables:

#!/bin/bash
echo "Enter first and last name:"
read FIRST LAST
echo "First: $FIRST"
echo "Last: $LAST"

# Input: "John Smith" -> FIRST=John, LAST=Smith
# Input: "John Paul Smith" -> FIRST=John, LAST="Paul Smith"

Extra words go into the last variable.

Exercise: Read User Input

Simulate reading input by setting a variable:

Reading into an Array

Read space-separated values into an array:

#!/bin/bash
read -p "Enter fruits (space-separated): " -a FRUITS

echo "You entered ${#FRUITS[@]} fruits:"
for fruit in "${FRUITS[@]}"; do
    echo "  - $fruit"
done

Using a Custom Delimiter

Read until a specific character:

#!/bin/bash
# Read until a comma
read -d ',' -p "Enter text (end with comma): " TEXT
echo "You entered: $TEXT"

The IFS Variable

IFS (Internal Field Separator) controls how read splits input:

#!/bin/bash
# Read CSV data
LINE="John,25,Engineer"
IFS=',' read -r NAME AGE JOB <<< "$LINE"
echo "Name: $NAME, Age: $AGE, Job: $JOB"

Raw Mode with -r

Always use -r to prevent backslash interpretation:

# Without -r (backslash is interpreted)
echo "Enter path:"
read PATH_VAR
# Input: C:\Users\name → PATH_VAR becomes "C:Usersname"

# With -r (backslash is literal)
read -r PATH_VAR
# Input: C:\Users\name → PATH_VAR becomes "C:\Users\name"

Best practice: Always use read -r unless you specifically need backslash interpretation.

Yes/No Confirmation

A common pattern for confirmations:

#!/bin/bash
read -p "Are you sure? (y/n): " -n 1 -r
echo
if [[ $REPLY =~ ^[Yy]$ ]]; then
    echo "Proceeding..."
else
    echo "Cancelled."
fi

Menu Selection

Create interactive menus:

#!/bin/bash
echo "Select an option:"
echo "1) Option One"
echo "2) Option Two"
echo "3) Exit"
read -p "Enter choice [1-3]: " CHOICE

case $CHOICE in
    1) echo "You chose Option One" ;;
    2) echo "You chose Option Two" ;;
    3) echo "Goodbye!" ;;
    *) echo "Invalid option" ;;
esac

The select Command

An easier way to create menus:

#!/bin/bash
PS3="Select a fruit: "    # Custom prompt
select FRUIT in "Apple" "Banana" "Cherry" "Quit"; do
    case $FRUIT in
        "Apple")  echo "You picked an apple!" ;;
        "Banana") echo "You picked a banana!" ;;
        "Cherry") echo "You picked a cherry!" ;;
        "Quit")   break ;;
        *)        echo "Invalid option" ;;
    esac
done

Reading from a File

Use redirection to read from files:

#!/bin/bash
# Read first line of a file
read -r FIRST_LINE < /etc/hostname
echo "Hostname: $FIRST_LINE"

# Read all lines
while read -r LINE; do
    echo "Line: $LINE"
done < file.txt

Exercise: Parse Delimited Data

Work with delimited input:

Best Practices

1. Always use -r to prevent backslash interpretation
2. Use -p for prompts instead of separate echo
3. Set timeouts for non-critical input with -t
4. Hide passwords with -s
5. Validate input before using it
6. Provide default values when appropriate

#!/bin/bash
# Good read practices

# With all best practices
read -rp "Enter username: " USERNAME
read -rsp "Enter password: " PASSWORD
echo

# With timeout and default
read -rt 10 -p "Enter name [Guest]: " NAME
NAME="${NAME:-Guest}"

# Validate input
while true; do
    read -rp "Enter a number: " NUM
    if [[ "$NUM" =~ ^[0-9]+$ ]]; then
        break
    fi
    echo "Invalid input. Please enter a number."
done

Key Takeaways

• read pauses the script to get user input
• Use -p "prompt" to display a prompt
• Use -s for password (hidden) input
• Use -t N for timeout after N seconds
• Use -n N to read only N characters
• Always use -r for raw input (no backslash interpretation)
• Use -a array to read into an array
• Change IFS to parse delimited data
• select creates interactive menus easily