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get previous month in shell script

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Aadkdev
Last edited Jan 18, 2016
Created on Jan 18, 2016

This shell script calculates the previous month for a given date, storing the result in a text file for later use. It reads a year and month from either command-line arguments or a previously saved file, then uses the GNU `date` command with the `--date` option to subtract one month from the 15th day of the specified month. The script writes the computed year and month back to a file named with a `last_` prefix, enabling sequential month calculations across runs. It relies on Bash parameter expansion for string slicing and file redirection for persistence.

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