Bash script to find and change file extensions recursively

Question

I want to put together a small script that changes the file extension of all the files in a directory that have a certain extension, such as .png or .gif.

My thought is that the script just take 2 arguments at execution. One being the extension to change and the second being the extension to change it to.

Originally I was thinking I would use read to get the target directory but that makes this too complicated so instead I am just making it work in the current directory. I am running Debian 9 so the rename command is not available.

This works with fixed content (txt to rdf):

$ find -depth -name "*.txt" -exec sh -c 'mv "$1" "${1%.txt}.rdf"' _ {} \; 

however, I cannot figure out how to change the extensions to the content of variables that inherit the passed arguments. these will be $1 $2 by default but when I change it as below, it does not work.

$ find -depth -name "*.$1" -exec sh -c 'mv "$1" "${1%.$1}.$2"' _ {} \; 

This example just appends a . to the end of all the matching files. What am I missing here?

Answer 1

#!/bin/sh find . -depth -name "*.$1" -exec sh -c ' from=$1 to=$2 shift 2 for pathname do mv "$pathname" "${pathname%.$from}.$to" done' sh "$1" "$2" {} + 

This is letting the internal script take the filename suffixes as parameters as well as a list of pathnames to change. In the internal script, you extract the two suffixes and shift them off the list of arguments, then loop over the patnames given to the script from find.

Less efficient (one invocation of sh -c per pathname instead of looping over a batch of them):

#!/bin/sh find . -depth -name "*.$1" -exec sh -c 'mv "$3" "${3%.$1}.$2"' sh "$1" "$2" {} ';' 

As a side note: Do make it a habit to use sh or find-sh or some other relevant name for the zeroth argument to the internal script. This argument is used in error messages from the script and having the error message come from _ might be confusing under some circumstances.