How does a pipe work in Linux?

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If you want to redirect the output of one program into the input of another, just use a simple pipeline:

program1 arg arg | program2 arg arg

If you want to save the output of program1 into a file and pipe it into program2, you can use tee(1):

program1 arg arg | tee output-file | program2 arg arg

All programs in a pipeline are run simultaneously. Most programs typically use blocking I/O: if when they try to read their input and nothing is there, they block: that is, they stop, and the operating system de-schedules them to run until more input becomes available (to avoid eating up the CPU). Similarly, if a program earlier in the pipeline is writing data faster than a later program can read it, eventually the pipe’s buffer fills up and the writer blocks: the OS de-schedules it until the pipe’s buffer gets emptied by the reader, and then it can continue writing again.

EDIT

If you want to use the output of program1 as the command-line parameters, you can use the backquotes or the $() syntax:

# Runs "program1 arg", and uses the output as the command-line arguments for
# program2
program2 `program1 arg`

# Same as above
program2 $(program1 arg)

The $() syntax should be preferred, since they are clearer, and they can be nested.

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