Question

I have a closed program (namely Intersystems ‘csession’ Cachédb terminal) that will write to a file given as a parameter. It do so several times, as then returns. Each time, the given file is overwritten, so at the end, I only get the last result…

I had the idea that it might be possible to trick and give a special pseudo-file as a parameter, that would act as a proxy and append what is written into it into another file.

create proxyfile as >> realfile
cat "Hello" > proxyfile
cat "Bye" > proxyfile
cat realfile
Hello
Bye

Does anyone think this might be doable, possibly using a little utility ?

Answer 1

You can use a FIFO file (named pipe) for this purpose. To see how they work, open up two terminal windows. In one, do

cd /tmp
mkfifo pipe
tail -f pipe

and in the other

cd /tmp
echo "Hello" > pipe
echo "Bye" > pipe

For the actual problem, let your application write to the FIFO and use tail -f pipe > outputfile in the background to gather the results into outputfile.