Pipelines
Learn how to combine several programs using a pipeline.
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The redirection operators are useful when we save data for manual analysis or processing. When we want to process data with another program, storing them in temporary files is inconvenient. Managing these files takes extra effort. We should remember their paths and remove them after usage.
Unix provides an alternative solution for transferring text data: a pipeline. This mechanism shares data between programs by passing messages. It doesn’t use the file system.
How pipelines work
The following example demonstrates how pipelines work. Let’s suppose that we are looking for information about the Bash license. The Bash documentation has it. Therefore, we call the grep
utility to parse documentation files this way:
grep -R "GNU" /usr/share/doc/bash
Another source of the Bash license information is the info
help page. We can take this information and transfer it to the grep
utility. The pipeline does this job. It takes the output of one program and sends it to the input of another one. The following command accomplishes this for info
and grep
programs:
info bash | grep -n "GNU"
Run the commands discussed in this lesson in the terminal below.
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