Using `find` for array jobs

[wwarriner]

What would you like to see added?

We can use find to determine how many files or directories are present in a given directory.

Files: find <containing-directory> -type f -name "<glob>"
Immediate subdirectories: find <containing-directory> -mindepth 1 -maxdepth 1 -type d -name "<glob>"
Recursive subdirectories: find <containing-directory> -mindepth 1 -type d -name "<glob>"
(more details: https://linuxhostsupport.com/blog/how-to-search-files-on-the-linux-terminal/)
(quotes are needed around glob: https://stackoverflow.com/questions/6495501/find-paths-must-precede-expression-how-do-i-specify-a-recursive-search-that/6495536#6495536)

Find can be helpful in determining how many things to iterate on with our array job. We can determine the upper limit of tasks using find ... | wc -l. The value can be used to give an upper limit statically by running once and making a note of the value. Or it can be used dynamically as part of a wrapper script around the payload script submitted with sbatch.

We recommend avoiding using ls for any post-processing or data aggregation operations such as wc -l or grep. The combination of ls and these tools can produce unexpected results.

[wwarriner]

There would be two parts to this.

1. Add information about find to the shell page.
2. Add a segment in our array tutorial about how to use find for that use case.

[wwarriner]

Related to #693

[wwarriner]

Add a header and content for "Search for files (find)" to https://docs.rc.uab.edu/workflow_solutions/shell/ after grep.