accessing the shell from PD

I find this sort of expected with large amounts of text being printed. Could you confirm what commands you use to trigger the issue? Also, can you try following the instructions here to upgrade to Pd 0.51 and see if the problem persists?

You should recompile your external after the update, as I am not 100% sure I preserved binary compatibility.

Do you need the current date or a monotonic time since the start of the script? The latter can be obtained with the [timer] object.

You can also do this:

copy this zip archive to the board, it provides pdsend which allows to send messages to pd from outside Pd.
Then run

unzip pdutils.zip
mv pdsend pdreceive /usr/local/bin

Then create a file like this called get_time.sh in your project:

#!/bin/bash

# do magic here to get time into variable TIME
TIME=$(date +%Y.%m.%d-%T)
# send TIME to Pd's netreceive
echo $TIME | pdsend 9999 localhost udp 2>/dev/null

Then you can have a patch like the attached one (with a suitable interval in the metro):

This patch executes get_time.sh which in turn sends the current time to pd via pdsend.

Nice workaround!
But since I need a bang on every second, should I write a shell script (or whatever) that sends directly the time on seconds to Pd?

Nice one, it probably works just fine, the issue is that time() will call into the Linux kernel and as it is called from within the audio thread it breaks the real-time guarantees of Bela, hence the "mode switch" warning.

You have several options:

• start up a thread and call time() in there, have the audio thread print the result that was obtained from the other thread. If you don't want the other thread to be polling all the time, you'll need to trigger a time() call in the other thread when you receive a bang, then set a pd timer (I believe that's what it's called?) a few ms later that reads the up-to-date result of time when it's ready and sends it out of the output. This is the most generally-applicable version, which will also improve real-time friendliness of your external when running outside Bela. It may get complicated because on a multi-core processor you'll need some way of guaranteeing memory coherence so that the audio thread never sees a corrupted version of the time and has a way of knowing for sure whether it's been updated.
• instead of calling time(), call __wrap_time(). This is a function provided by Xenomai's libcobalt that is safe to call from the audio thread. Before you call it you may have to declare it (depending on your compiler's options):

  extern time_t __wrap_time(time_t *tloc);

  I don't think you have to change your linker flags. You should be able to build it like this and at runtime it will be resolved because libcobalt is already loaded by the Bela binary.
• leave the external exactly as it is. Bang it only once at the beginning of the script to get the time, ignore the mode switch message. Then use bangs to the [timer] object to measure elapsed time while the program is running. I appreciate this may have accuracy implications for long running patches (which you can obviate to by resetting the timer every so often) and if you need the year/month/day/hour/min/sec the previous option may be easier.