[EMAIL PROTECTED] wrote:
> Hello, All:
>
> I need to check files to make sure that they are .gif, .jpg, or .png
> graphic files before processing them. How can I verify that?
>
> e.g., In unix, the 'type' command returns the file's type.
>
all .gif, .jpg and .png file have a special header id that identify their
types. for example, starting from the 7th byte of a JPEG file, you should
see the special id as: ox4A 0x46 0x49 0x46 and 0x00, the following checks
for that:
my $t = undef;
my($one,$two,$three,$four,$five);
open(IMG,"/tmp/showban.jpg") || die $!;
sysread(IMG,$t,6); #-- discard the first 6 bytes
#-- read the next five bytes
sysread(IMG,$one,1);
sysread(IMG,$two,1);
sysread(IMG,$three,1);
sysread(IMG,$four,1);
sysread(IMG,$five,1);
#-- unpack them and make sure they are the right magic ID
#-- you can get the id from the JPEG specification
if(unpack("C",$one) == 74 && unpack("C",$two) == 70 &&
unpack("C",$three) == 73 && unpack("C",$four) == 70 &&
unpack("C",$five) == 0){
print "jpeg\n";
}else{
print "not jpeg\n"
}
close(IMG);
similarly, for a .gif file, use the following:
open(IMG,"/tmp/res0.gif") || die $!;
sysread(IMG,$t,3);
($one,$two,$three) = unpack("CCC",$t);
if($one == 71 && $two == 73 && $three == 70){
print "gif\n";
}else{
print "not gif\n";
}
close(IMG);
you can do pretty much the same thing to png file. just go to google, search
for png specification, find out what the maigc id should look like and just
code it according to the specfication.
david
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