What Is a Practical Use for Standard Input in a Data Tool?
From the earlier reference collection. Read the current software blog.
Accepting piped data makes a small command-line tool easy to compose, while an explicit file option keeps named inputs clear and repeatable.
Let the tool fit into a pipeline
Standard input gives a data tool a simple way to receive the output of another program. A user can fetch a feed, decompress it, and pass the result to a validator without first choosing a permanent intermediate filename. For example, curl -fsS https://example.invalid/feed.csv | feed-check can make the validator the next step in a larger shell workflow. The address is illustrative; the important design point is that the tool reads bytes or text from its input stream.
Keep named files explicit
Pipes are useful for temporary or generated data, but a named file is often easier to inspect, reuse, or mention in a bug report. Support an option such as --input path for that case. Make the two modes unambiguous: when --input is present, read that path; otherwise, read standard input. Avoid silently guessing based on whether a filename happens to follow the command, unless positional input is part of the documented interface.
A practical invocation might be feed-check --input yesterday.csv. Its piped counterpart might be cat yesterday.csv | feed-check. Both should reach the same parser and produce the same validation result.
Design the stream boundary carefully
Read the stream once and pass its contents into the normal parsing and validation path. This keeps file handling from becoming a separate, subtly different implementation. If the input can be large, process it incrementally where the format permits, rather than collecting everything in memory. Report read failures distinctly from malformed records so a broken pipe or inaccessible file is not mistaken for a data error.
Reserve standard output for the result when users may pipe that result onward. Put progress and diagnostic messages on standard error. Otherwise, a friendly status line can accidentally become an invalid row in the next program's input.
Make the contract visible
Help text should state the default clearly: for example, “Read from standard input unless --input FILE is supplied.” Show one pipeline and one named-file example. If the program needs seekable input or must inspect data twice, explain that constraint or spool the stream into a controlled temporary file.
This small interface choice gives a tool both composability and inspectability. Users can prototype with a pipe, save a troublesome input under a stable name, then rerun the same validator with --input while diagnosing a failure.