bash - check if file is png file using magic numbers

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[ "$(xxd -s 0 -l 4 -p "/path/to/image.png")" = "89504e47" ] && echo "image.png is PNG file" || echo "image.png is not PNG file"

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if [ "$(xxd -s 0 -l 4 -p "/path/to/image.png")" = "89504e47" ]
then
	echo "image.png is PNG file"
else
	echo "image.png is not PNG file"
fi

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function is_png()  # args: file_path
{
	#                               . P N G  (as chars)
	#                               89504e47 (in hex)
	[ "$(xxd -s 0 -l 4 -p "$1")" = "89504e47" ] && return 0 || return 1
}


# Usage example:

is_png "/path/to/image.png" && echo "image.png is PNG file" || echo "image.png is not PNG file"

# or:

if is_png "/path/to/image.png"
then
    echo "image.png is PNG file"
else
    echo "image.png is not PNG file"
if