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I am following a guide to learn terminal commands and have encountered the use of hyphens to refer to stdin in the following command used to find all files named 'file-A' within the directory playground. I understand it's usage to refer to the files found by the find command which are of course piped to tar and set to be read as a file using the --files-from= option. I do not understand it's usage in defining the intermediary name of the archive before being renamed by the gzip command.

 find ./playground -name 'file-A' | tar -cf - --files-from=- | gzip playground.tgz

Would the value of stdin not be a list of paths defined in the stdin file? if so how can this be an acceptable name for the archive?

Thanks

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I can't find it in the tar manual. However - is often used by tools as a pseudo-filename referring to stdin or stdout. tar is using if for both. -f - saying output to stdout and --files-from=- saying get a list of file-names from stdin. The in and out are implied, these options expect an output and input respectively.

Also: gzip is not renaming. And there are no temporary files, data is passed via pipes.

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  • Ah I see thank you so it does not create a filename with the value of Stdin but send a the archive to stdout. Very helpful, have a nice day
    – nrmad
    Dec 29, 2020 at 12:58

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