GIF Graphics Interchange Format

SIGNATURE = bytes.fromhex("474946383761")
OFFSET = 0

def is_gif(path: str) -> bool:
    with open(path, "rb") as f:
        f.seek(OFFSET)
        head = f.read(len(SIGNATURE))
    return head == SIGNATURE

const SIGNATURE = [0x47, 0x49, 0x46, 0x38, 0x37, 0x61];
const OFFSET = 0;

// bytes: a Uint8Array / Buffer holding the start of the file
export function isGif(bytes) {
  return SIGNATURE.every((byte, i) => bytes[OFFSET + i] === byte);
}

package fileid

import "bytes"

var isgifSignature = []byte{0x47, 0x49, 0x46, 0x38, 0x37, 0x61}

const isgifOffset = 0

func IsGif(b []byte) bool {
	end := isgifOffset + len(isgifSignature)
	if len(b) < end {
		return false
	}
	return bytes.Equal(b[isgifOffset:end], isgifSignature)
}

const SIGNATURE: &[u8] = &[0x47, 0x49, 0x46, 0x38, 0x37, 0x61];
const OFFSET: usize = 0;

fn is_gif(bytes: &[u8]) -> bool {
    bytes.get(OFFSET..OFFSET + SIGNATURE.len()) == Some(SIGNATURE)
}

<?php
$signature = "\x47\x49\x46\x38\x37\x61";
$offset = 0;

function is_gif(string $bytes): bool {
    global $signature, $offset;
    return substr($bytes, $offset, strlen($signature)) === $signature;
}