Concept: Pipelines and Command Lists #714
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| The pipe symbol (`|`) connects the output of one command to the input of another. | ||
| `cut` reads the output of `cat`, and `sort` reads the output of `cut`. |
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Do you want to take a step back and mention how many commands read from STDIN (and/or a file) and write to STDOUT? Introduce STDIN/STDOUT?
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Right, I'll do a "sneak preview" of I/O, with a promise of more to come in a later concept.
Co-authored-by: Isaac Good <[email protected]>
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@IsaacG can I get your opinion on the I/O blurb please? |
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Still approved.
There is also one place where we have a sentence per line broken at a comma, I think that is kind of a nice thing to do for longer sentences anyway. But it is inconsistent, as there is one that is done this way but another that could benefit the same way.
Not a big deal, just a note here.
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Sorry for missing that. It's been a hectic two weeks. The blurb looks good! Do you still want nitpick improvement suggestions? |
Always! |
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| # Pipelines and Command Lists | |||
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| We have seen how to write simple commands, where a command is followed by arguments. | |||
| # Pipelines and Command Lists | ||
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| We have seen how to write simple commands, where a command is followed by arguments. | ||
| Now we will see how to make more complex commands by composing simple commands. |
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"by combining simple commands"
Composing means writing. Composing simple commands gives you simple commands.
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| ## Input and Output | ||
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| Before we start, a quick introduction to input/output. |
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"to input and output (I/O or IO)"
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| Before we start, a quick introduction to input/output. | ||
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| Processes have "standard I/O channels". |
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I/O should be defined before being used.
Channels might be worth definig.
"Processes interact with other processes (or users) by transmitting data across channels. Data going into the process is input (such as a user typing numbers into a calculator) while data coming out of the process is output (such as the result of a calculation or an error message)."
| * A process can consume _input_ on "stdin". | ||
| * A process can emit _output_ on "stdout". | ||
| * A process can emit _error output_ on "stderr". |
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I would expand those first. "on stand out (stdout)"
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This might be a good place to explain how multiple, distinct channels (STDOUT and STDERR) can both write to the same destination (the terminal) then mention later how the pipe redirects one but not the other.
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| ## Pipelines | ||
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| This is one of the "killer features" of shell programming. |
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s/This/Pipelines/
"This" references a prior idea. A new paragraph should generally not be attached to a prior idea.
| ## Pipelines | ||
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| This is one of the "killer features" of shell programming. | ||
| Pipelines allow you create sophisticated transformations on a stream of text. |
| cat /etc/passwd | cut -d : -f 1 | sort | ||
| ``` | ||
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| The pipe symbol (`|`) connects the output of one command to the input of another. |
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stderr was defined out "output" (error output) earlier. One might think the | would redirect STDERR
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| A command list is a sequence of pipelines separated by `;` (or newline), `&&` or `||`. | ||
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| * `A; B` is a command list where `B` executes after `A` has completed. |
| #### Reading blocks of lines from a file | ||
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| Suppose you have a data file containing data about triangles, | ||
| and a triangle is represented by three separate lines holding the sides of the triangle. |
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