Determine if received data is PostScript or PCL

Question

I have a service that receives printer data via tcp/ip. When the data is received, is there reliable, efficient way to examine the data stream and determine if the data is PostScript vs PCL data? For example, are there characters I could look for at the beginning of the data stream to indicate the format?

Answer 1

Postscript data must begin with "%!ps" or "%!PS" - it may be a longer readable string like "%!PS-Adobe-3.0" - but that is basically this.

Most likely PCL have a similar signature - I remember seeing it in the past.

Answer 2

I would probably just count the number of escape characters in the file. PCL will have gobs of them. Postscript will have gobs of % signs. That isn't a perfect solution, but it's dead simple and I'll bet it would actually be quite reliable.

The only "real" way I can see doing this is to actually parse the PCL and parse the postscript and see which one works.

Answer 3

I'll add my 2¢.

Like others have mentioned here, your first stab at programmatically identifying the document would be to look at the first two characters. If it starts with %!, it is PostScript, if it starts with an escape character (hex 1B, oct 033, ascii 27), as very likely PCL will start with PCL commands, then it is PCL. This will likely resolve 99% of the documents you need to process. If it still isn't known, then you can search the document for a showpage string. If it's PostScript, it has to have a showpage to render the page. If you can't find one, and if there are any escape characters in the file, you know it is PCL, and you can err on the side of PCL if there is no showpage, and there is no escape characters, because raw text files are valid PCL and printers can blort them out as they come.

Answer 4

According to the PCL 5 General Printing FAQs PCL files should start with ESC "E". I assume another ESC sequence must follow. So my guess is that files starting with bytes 1B 45 1B are most likely PCL files. This leaves PCL files unrecognized which don't adhere to this rule.

In my use case it's macOS that always produces PCL with the ESC E at the beginning.