Bash — Input and Output

Reading input

#!/bin/bash

# Basic input
read -p "Enter name: " name
echo "Hello, $name!"

# Silent input (for passwords)
read -sp "Enter password: " pass
echo

# With timeout
read -t 5 -p "Quick! Enter something: " input

Output redirection

#!/bin/bash

# Redirect stdout
echo "Hello" > file.txt      # Overwrite
echo "World" >> file.txt     # Append

# Redirect stderr
command 2> error.txt

# Redirect both
command > output.txt 2>&1
command &> output.txt

Here documents

#!/bin/bash

cat << EOF
Name: Alice
Age: 30
City: NYC
EOF

# With variable expansion
cat << EOF
Today is $(date)
User is $USER
EOF

File reading

#!/bin/bash

# Read entire file
content=$(cat file.txt)

# Read line by line
while IFS= read -r line; do
    echo "$line"
done < file.txt

Piping

#!/bin/bash

# Pipe output to next command
ls -la | grep ".txt" | wc -l

# Process substitution
diff <(ls dir1) <(ls dir2)

Mini Practice

Write Bash code that:

1. Reads user input with read
2. Redirects output to a file
3. Uses a here document
4. Reads a file line by line

Up Next

In the next lesson, you'll learn about Pipes — chaining commands together.