Appending a string before file extension in Bash script

Question

I need to add a number just before the extension of the files with a Bash script. For example, I want to convert a file name like abc.efg to abc.001.efg. The problem is that I don't know what is the extension of the file (it is one of the parameters of the script).

I was looking for the quickest way of doing this.

Answer 1

You can do something like this:

extension="${file##*.}"                     # get the extension
filename="${file%.*}"                       # get the filename
mv "$file" "${filename}001.${extension}"    # rename file by moving it

You can see more info about these commands in the excellent answer to Extract filename and extension in Bash.

Test

$ ls hello.*
hello.doc  hello.txt

Let's rename these files:

$ for file in hello*; do ext="${file##*.}"; filename="${file%.*}"; mv "$file" "${filename}001.${ext}"; done

Now check whether renaming worked as expected:

$ ls hello*
hello001.doc  hello001.txt

Answer 2

sed 's/\.[^.]*$/.001&/'

you can build your mv cmd with above one-liner.

example:

kent$  echo "abc.bar.blah.hello.foo"|sed 's/\.[^.]*$/.001&/' 
abc.bar.blah.hello.001.foo

Answer 3

If your file extension is in a variable EXT, and your file is in a variable FILE, then something like this should work

EXT=ext;FILE=file.ext;echo ${FILE/%$EXT/001.$EXT}

This prints

file.001.ext

The substitution is anchored to the end of the string, so it won't matter if your extension appears in the filename. More info here http://tldp.org/LDP/abs/html/string-manipulation.html