Bash User Input and Output

Every useful script either displays information to the user or accepts information from the user. Bash provides straightforward built-in tools for both input and output operations.

Output with echo

The echo command prints text to the terminal screen. It is the most commonly used output command in Bash.

#!/bin/bash
echo "Welcome to eStudy247 Bash Course"

Output:

Welcome to eStudy247 Bash Course

echo Options

Escape Characters with echo -e

#!/bin/bash
echo -e "Name:\tAlice\nCity:\tDelhi"

Output:

Name:   Alice
City:   Delhi

Output with printf

The printf command gives more precise control over output formatting. It works like printf in C programming.

#!/bin/bash
printf "Name: %s\nAge: %d\n" "Alice" 25

Output:

Name: Alice
Age: 25

Format Specifiers for printf

Reading User Input with read

The read command waits for the user to type something and press Enter. The typed value gets stored in a variable.

#!/bin/bash
echo "Enter your name:"
read username
echo "Hello, $username!"

Terminal interaction:

Enter your name:
Alice
Hello, Alice!

read with Prompt (-p flag)

Instead of using a separate echo line, the prompt can be included directly in the read command using -p.

#!/bin/bash
read -p "Enter your city: " city
echo "You live in $city."

Output:

Enter your city: Mumbai
You live in Mumbai.

read with Silent Input (-s flag)

The -s flag hides the input as the user types. This is commonly used for passwords.

#!/bin/bash
read -sp "Enter password: " pass
echo ""
echo "Password accepted."

The echo "" after the read adds a new line because the -s flag suppresses the automatic newline.

Reading Multiple Values in One Line

Multiple variables can be filled from a single read command by separating values with spaces.

#!/bin/bash
read -p "Enter first and last name: " fname lname
echo "First: $fname"
echo "Last:  $lname"

Terminal interaction:

Enter first and last name: John Doe
First: John
Last:  Doe

Reading Input with a Timeout (-t flag)

The -t flag sets a time limit in seconds for the user to respond.

#!/bin/bash
read -t 5 -p "Press Enter within 5 seconds: " answer
if [ $? -ne 0 ]; then
  echo "Time expired!"
fi

Input and Output Flow Diagram

┌────────────────────────────────────────────────┐
│              Script Execution Flow             │
│                                                │
│  Script starts                                 │
│        │                                       │
│        ▼                                       │
│  echo "Enter name:"  ──► Shows text on screen  │
│        │                                       │
│        ▼                                       │
│  read name           ──► Waits for keyboard    │
│        │                                       │
│        ▼                                       │
│  echo "Hello, $name" ──► Shows result          │
└────────────────────────────────────────────────┘

Reading Input from a File

The read command can also read content line by line from a file using a while loop.

#!/bin/bash
while read line
do
  echo "Line: $line"
done < fruits.txt

If fruits.txt contains:

Apple
Banana
Mango

Output:

Line: Apple
Line: Banana
Line: Mango

Practical Example – Simple User Form

#!/bin/bash
echo "===== Student Registration ====="
read -p "Enter student name: " sname
read -p "Enter student age:  " sage
read -p "Enter student city: " scity
echo ""
echo "--- Registration Details ---"
printf "Name : %s\n" "$sname"
printf "Age  : %d\n" "$sage"
printf "City : %s\n" "$scity"

Output:

===== Student Registration =====
Enter student name: Ravi
Enter student age:  22
Enter student city: Pune

--- Registration Details ---
Name : Ravi
Age  : 22
City : Pune

Key Takeaways

• Use echo for simple output and printf for formatted output.
• Use read to accept input from the user.
• The -p flag adds a prompt message directly to the read command.
• The -s flag hides typed input — useful for passwords.
• The -t flag adds a timeout to the input.
• The read command can also process file contents line by line inside a loop.