String#hex

Returns Integer· Updated May 19, 2026· String Methods

ruby

Signature

str.hex → Integer

No parameters. Parses the leading hexadecimal digit sequence from str and returns it as an Integer.

What It Does

String#hex scans the string from left to right for a sequence of hexadecimal characters (0–9, a–f, A–F). It accepts an optional sign (+ or -) at the start and an optional 0x prefix (case-insensitive). Parsing stops at the first non-hex character. The rest of the string is ignored.

This makes it useful for reading hex values from configuration files, parsing hex color codes, and interpreting hex-encoded data from hardware registers or network packets.

Return Values

Condition	Return value
Leading hex digits found	Integer (base 16)
No leading hex digits	`0`
Empty string	`0`
With `0x`/`0X` prefix	Integer (prefix is ignored)
With sign (`+`/`-`)	Signed integer

Examples

Basic conversion

"ff".hex          # => 255
"0xff".hex        # => 255
"-0xff".hex       # => -255
"aB".hex          # => 171
"0xDEAD".hex      # => 57005

The 0x prefix is optional. Both "ff" and "0xff" produce the same result.

Parsing stops at non-hex characters

"10xyz".hex       # => 16
"0xFFG".hex       # => 255

The moment a character that isn’t a valid hex digit appears, parsing stops. The G in "0xFFG" is simply ignored.

Hex Color to RGB

A common use case is extracting RGB channels from a hex color code:

def hex_to_rgb(hex_str)
  hex_str.delete('#').hex
end

hex_to_rgb("#ff5733")  # => 16735475

Extract individual channels by bit-shifting:

def hex_to_channels(hex_str)
  hex = hex_str.delete('#').hex
  r = (hex >> 16) & 0xff
  g = (hex >> 8)  & 0xff
  b =  hex        & 0xff
  [r, g, b]
end

hex_to_channels("#ff5733")  # => [255, 87, 51]

String#hex vs Integer()

Unlike Integer(), String#hex never raises an exception — if no leading hex is found, it silently returns 0:

Integer("0x10")   # => 16
"0x10".hex        # => 16

Integer("xyz")    # => ArgumentError
"xyz".hex         # => 0

Use Integer() when you want strict parsing and an exception on bad input. Use String#hex when you want to silently skip over non-numeric strings.