17.24 Replace Regexp in a File

20210304 We can replace strings within a line that match a regular expression using perl. For example, to replace strings that are at the beginning of a line that contain two asterisks, then an 8 digit date, then two more asterisks and a space, with an inline call to an R function in a bookdown document:

$ perl -pi.bak -e 's|^\*\*(\d{8})\*\* |`r#cite_date($1)` |' chapt1.Rmd
$ meld chapt1.Rmd.bak chap1.Rmd

In this example -i is used to do the replacement in place and .bak is added so that the original file kept as a backup in case anything should go wrong. We can use meld to compare the files to confirm all works as expected.

Once we are comfortable and have tested the process, we can repeat this for all Rmd files int eh current directory:

$ perl -pi.bak -e 's|^\*\*(\d{8})\*\* |`r#cite_date($1)` |' *.Rmd

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