Menu
Say I have three programs: generator, that produces input data fed to processor and verifier that can check if processor output is correct for given input (so it needs both files).
What I currently do is:
generator > in.txt && processor < in.txt > out.txt && cat in.txt out.txt | verifier
Is it possible to achieve the same result without using explicit files? I've read about duplicating input using tee and and process substitution, but I didn't find a way to collect both streams into single one for final step.
358
You can make it do so by using the pipe character '|'. Pipe is used to combine two or more commands, and in this, the output of one command acts as input to another command, and this command's output may act as input to the next command and so on.
stdin − It stands for standard input, and is used for taking text as an input. stdout − It stands for standard output, and is used to text output of any command you type in the terminal, and then that output is stored in the stdout stream.
Pipe shell command It is used to pipe, or transfer, the standard output from the command on its left into the standard input of the command on its right. # First, echo "Hello World" will send Hello World to the standard output. # Next, pipe | will transfer the standard output to the next command's standard input.
I have not tested this, but try:
{ generator | tee /dev/stderr | processor ; } 2>&1 | verifier
This will redirect a copy of generator output to stderr. Then run processor on stdout of generator. Then combine both & pipe to verifier.
However, this cannot guarantee the order, in which lines from generator & processor would reach verifier.
Alternately, you can try process substitution like below:
( generator | tee >(processor) ) | verifier
If you don’t want to create real files on your slow hard-disk, you can use FIFOs (First In First Out), which are also called named pipes, because of their behaviour.
mkfifo myfifo
generator | tee myfifo | processor | verifier myfifo
This streams the generated content to tee, which duplicates it to myfifo and to stdout, which is piped through the processor to the verifier. And the verifier also gets the stream from myfifo.
22
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
