How does a pipe work in Linux?

Question

How does piping work? If I run a program via CLI and redirect output to a file will I be able to pipe that file into another program as it is being written? Basically when one line is written to the file I would like it to be piped immediately to my second application (I am trying to dynamically draw a graph off an existing program). Just unsure if piping completes the first command before moving on to the next command. Any feed back would be greatly appreciated!

Accepted Answer

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.

How does a pipe work in Linux?

Solution

Problem