How to processing "tr" command inside all files in a folder?

Question

I can do this like for one file:

tr -cs "[:alpha:]" "\n" < some_file

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But, how to processing tr to all files in a folder recursive?

tr -cs "[:alpha:]" "\n" < /some_folder

or

tr -cs "[:alpha:]" "\n" < *

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It gives me an error like:

tr: read error: Is a directory

Answer 1

Use find and xargs to pipe the file contents into tr like so:

find some_folder -type f -print0 | xargs -0 cat|tr -cs "[:alpha:]" "\n"