# Channeling two named PIPEs with a GNU Radio flowgraph | String transmitted on one end does not reach the other end

1) I created two named PIPEs:

$$mkfifo pipe_in$$ mkfifo pipe_out


2) Then connected pipe_in to pipe_out with the following GNU radio flowgraph:

File Source config:

• Repeat: No
• Vec Length: 1 (default setting)
• Add begin tag: pmt.PMT_NIL (default setting)

File Sink config:

• Unbuffered: Off
• Vec Length: 1 (default setting)
• Append file: Overwrite

3) Finaly, I start running the flowgraph, then write a string to pipe_in hoping to see it reach pipe_out by running the following two commands in separate terminals:

TERM2 $tail -f pipe_out  and TERM1$ echo 'hello world!' > pipe_in


Unfortunately the string never reaches pipe_out. Can someone shed some light please?

• Can you upload a higher resolution image? – rmagno Mar 11 at 11:59
• @rmagno, unfortunately that is currently not possible, afaik. It's a GNU Radio limitation... – fmagno Mar 11 at 12:09
• @rmagno are you and OP related? Yep, on GNU Radio 3.7, the GNU Radio Companion tool has a fixed rendering size, i.e. can't zoom (the picture would still be easier to read if it wasn't scaled up, but that's a different story) – Marcus Müller Mar 11 at 12:10
• @gmagno yep! The current development version on git does exactly that. Also, Qt5 instead of Qt4 for visualization widgets, and Py3 instead of Python2 (optional), better build system, you know, stuff like that :) – Marcus Müller Mar 11 at 12:15
• @rmagno an rmagno answering to an fmagno, I just liked that :) – Marcus Müller Mar 11 at 13:56

That's how tail works, it waits until the end to print the last n lines. If you use cat instead, it should work.