Creating a remote a file over serial using python

Question

I have a host connected to a Linux target over serial. The target is using the serial port for shell I/O. I need to save a text file on the target with contents from the host.

I thought I could get away with doing:

ser.write("cat > file.txt\n")
ser.write([contents I need to add to the file])
ser.write(chr(4))
ser.write(chr(4))

But the 's I'm sending aren't closing the file. I've tried a few variations of chr(4)... \x04, print, str =, and a few others, but they all fail the same way.

If I simulate this with minicom, and follow up sending the [contents...] with uploading a 2 byte file that holds 0x04 0x04, the file closes as expected.

I haven't tried opening the "EOF" file in python and sending it yet. I'll do it, I'm about out of options. But I'm new to python, so I must be doing something wrong.

Any obvious newb-fixing answer to this one?

Thanks.

first, make sure your [contents...] is terminated with a newline. Then maybe try adding ser.flush() at the end. — jwygralak67
– jwygralak67, Commented Aug 14, 2013 at 15:05
Did both of those (and also tried Ctrl-D Ctrl-D instead of newline, that should work too), but it's not closing the file. I need to go through minicom and type Ctrl-D to close it. — user2679165
– user2679165, Commented Aug 15, 2013 at 15:21

Sylvain Leroux · Accepted Answer · 2013-08-15 15:31:58Z

1

As a workaround, could you use a heredoc ?

ser.write("cat > file.txt << END_OF_FILE\n")
ser.write([contents I need to add to the file])
ser.write("\nEND_OF_FILE\n");

For a more robust solution, you should probably have to look at some file transfer protocol over serial line, like Kermit.

edited Aug 15, 2013 at 15:31

answered Aug 14, 2013 at 13:41

Sylvain Leroux

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5 Comments

user2679165 Over a year ago

Yes, I'm using that work-around now. It's likely that I could come up with an end-string that's unlikely to appear in the data I'm transferring, but I was still hoping that I could just simulate a couple Ctrl-D's somehow.

Sylvain Leroux Over a year ago

@user2679165 Even if there is a "magic" sequence of character, I don't think this is a viable solution anyway: maybe it would works for this particular file, but more generally, whatever is that sequence, the probability it appears in the transferred file is not nul. For a more robust approach, you will have to look a some protocol like the venerable Kermit. I edited my answer accordingly.

user2679165 Over a year ago

Unfortunately I can't assume kermit, ymodem, or any other protocol is available on the remote side. I don't have control over it. I can assume it has a file system I can write to, and cat, redirection, and pipes are available. Those are enough for me to do what I need to with minicom, I just need to figure out how in python.

Sylvain Leroux Over a year ago

@user2679165 Do you have an oscilloscope at hand? Is it possible that Minicom simulate the end-of-file by lowering down/raising up some control lines?

user2679165 Over a year ago

That would be pretty cool. But it also works correctly when I upload a file that has a couple Ctrl-D's (0x04 0x04) in it, and I don't think it's parsing file contents.

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