Change first character pattern in a file name without changing that same pattern elsewhere in the file name

Question

On a Linux server I have a directory full of files with digits for names. Some of the files start with two zeros such as 00305005. I am writing a bash shell script and one of the steps is to rename all of the files that start with 00 so they start with @0. The file I mentioned earlier would be @0305005.

The issue I am having is that when I try to rename the files I end up changing all instances of 00 in the file name to @0 like this: @0305@05. I have been using the following code and I don't know how to fix it:

for f in 00*; do mv "$f" "${f//00/@0}"; done

Answer 1

If you're stuck with shell magic then go a different path and try transforming the file name with a different tool, such as f.ex. sed

for f in 00*; do
  new_f=$( echo "$f" | sed 's/00/@0/' )
  echo mv "$f" "$f_new"
done

I've inserted the echo before the mv so that you can test first if the mvs look OK, before you wreck your files. You can then remove that echo.

Answer 2

When you use ${var//pattern/replacement}, the // means "replace all occurrences". In this case you only want to replace the first occurrence, so you can use just /. Or, you could be even more specific, and use /#, which will replace only at the beginning of the string; this shouldn't make a difference since you're only processing files that start with 00, but I'd be inclined to use it to make the goal explicit. Here's a demo:

$ f=00305005
$ echo "${f//00/@0}"    # // = replace all
@0305@05
$ echo "${f/00/@0}"     # /  = replace first one -- this does what you want
@0305005
$ echo "${f/#00/@0}"    # /# = replace at beginning -- this also does what you want
@0305005
$ g=90305005            # Let's test with a name that *doesn't* start with 00
$ echo "${g/00/@0}"     # / replaces the first match, no matter where it is in the string
90305@05
$ echo "${g/#00/@0}"    # /# does not replace if the beginning does not match
90305005

I'd also recommend using mv -i for any sort of bulk move/rename, to avoid data loss if there's a naming conflict or error. Thus, here's what I'd recommend:

for f in 00*; do mv -i "$f" "${f/#00/@0}"; done