How to trim the tail number of the file via shell script?

Question

I have the files as below. There are four files in total:

cert1.pem chain1.pem fullchain1.pem privkey1.pem

I want to trim the tail number of each file (1 here). How do I use a shell script to handle it automatically? I am familiar with some commands, but I think I am not good at writing shell scripts to handle this batch processing.

Answer 1

If the trailing number is a single digit, and they are all .pem files, you could use parameter expansion to strip the digit and extension, then replace the extension:

for file in cert1.pem  chain1.pem  fullchain1.pem  privkey1.pem
do
  mv "$file" "${file%%?.pem}.pem"
done

The parameter expansion works by removing the longest trailing match (%%) of any single character (?) followed by .pem; after that is done, we manually add back the .pem at the end.

Note that this would also rename files like certX.pem or fullchain-.pem, because the ? character expands to any single character.

This is made safer in the above example because I've manually listed the files to rename. You could alternatively use something like:

for file in *1.pem
do
  mv "$file" "${file%%?.pem}.pem"
done

... which loops explicitly over files with 1.pem at the end of their names.

Setup:

$ ls
cert1.pem  chain1.pem  fullchain1.pem  privkey1.pem

Execution:

$ for file in cert1.pem  chain1.pem  fullchain1.pem  privkey1.pem
  do 
    mv "$file" "${file%%?.pem}.pem"
  done

Result:

$ ls
cert.pem  chain.pem  fullchain.pem  privkey.pem