Kernel#putc

putc(obj) -> obj

Returns: Object · Updated March 13, 2026 · Kernel Methods

output io characters printing

The putc method outputs a single character to STDOUT. Unlike puts which outputs strings with a newline, putc writes exactly one character and returns the object that was passed to it.

How It Differs from puts

puts "hello"  # Outputs: hello\n and returns nil
putc "hello"  # Outputs: h and returns "hello"

puts "A"      # Outputs: A\n
putc "A"     # Outputs: A

Practical Examples

Basic Character Output

# Output a single character
putc "A"    # Prints: A

# With integers - outputs the character with that ASCII code
putc 65     # Prints: A (ASCII 65)
putc 97     # Prints: a (ASCII 97)
putc 10     # Prints: newline

# String input - only first character
putc "hello"  # Prints: h

Building Output Character by Character

# Create a progress indicator
progress = ["|", "/", "-", "\\"]
5.times do |i|
  print "\rProcessing #{progress[i % 4]}"
  putc "\r"  # Carriage return to overwrite
  sleep 0.5
end
puts "\nDone!"

Writing to a File

# Putc works with any IO object
File.open("output.txt", "w") do |f|
  putc f, "H"
  putc f, "i"
  putc f, "\n"
end
# File contains: Hi

Low-Level Character Handling

# Convert number to character
putc 0x41    # Hex 41 = 65 = 'A', outputs: A

# Binary data handling
bytes = [0x48, 0x65, 0x6C, 0x6C, 0x6F]
bytes.each { |b| putc b }
# Outputs: Hello

# Output character from variable
char = "X"
putc char  # Outputs: X

Color Output in Terminal

# ANSI escape codes for colors
RED = "\e[31m"
RESET = "\e[0m"

putc RED[0]
putc "R"[0]
putc RESET[0]
puts  # Newline to complete

Return Value

# putc returns the object passed to it
result = putc "hello"
puts result  # => hello

# This allows chaining (though unusual)
putc(putc("A"))  # Outputs: AA, returns "A"

Common Uses

putc is useful when you need:

Character-by-character output
Building output incrementally
Working with binary data
Low-level terminal operations

It’s a lower-level method than puts or print, giving you direct control over exactly what bytes are written to the output stream.