How to convert Hex to binary in PHP?

I’m trying to send 0x01 HEX as Byte using the socket_write($socket, XXXX , 1); function.

There is part of documentation:

“…If yes, server will reply to module 0x01, if not – replay 0x00. Server must send answer – 1 Byte in HEX format.”

Answer

There are multiple alternatives:

• When using the pack() function, the string argument to the H* format specifier should not include the 0x prefix.

  pack("H*", "01")
  

• To convert a single hex-number into a byte you can also use chr().

  chr(0x01)
  

  Here PHP first interprets the hex-literal 0x01 into a plain integer 1, while chr() converts it into a string. The reversal (for socket reading) is ord().

• The most prevalent alternative is using just using C-string escapes:

  "x01"
  

  Or in octal notation:

  "01"
  

• hex2bin("01") works just like pack("H*") here. And there’s bin2hex for the opposite direction.