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I have a script that writes to a named pipe and another that reads from the pipe. Occasionally, when starting the script I have noticed that the contents of the pipe exist from a previous run of the script. Is there a way to flush out the pipe at the beginning of the script?
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$1 means an input argument and -z means non-defined or empty. You're testing whether an input argument to the script was defined when running the script. Follow this answer to receive notifications.
A pipe in Bash takes the standard outputstandard outputStandard output (stdout) Standard output is a stream to which a program writes its output data. The program requests data transfer with the write operation. Not all programs generate output.https://en.wikipedia.org › wiki › Standard_streamsStandard streams - Wikipedia of one process and passes it as standard input into another process. Bash scripts support positional arguments that can be passed in at the command line.
From man bash : -s If the -s option is present, or if no arguments remain after option processing, then commands are read from the standard input. This option allows the positional parameters to be set when invoking an interactive shell. From help set : -e Exit immediately if a command exits with a non-zero status.
I think dd is your friend:
dd if=myfifo iflag=nonblock of=/dev/null
strace shows
open("myfifo", O_RDONLY|O_NONBLOCK)
and indeed doesn't even block on an empty fifo.
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You can read from the pipe until it is empty. This will effectively flush it.
Before you attempt this daring feat, call fcntl(mypipe, F_SETFL, O_NONBLOCK) (I don't know the shell-scripting equivalent) to make a read when the pipe is empty not hang your program.
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