Hi. Can someone tell me how to append an extension to all files in a folder.

I was thinking about writing a shell script that takes the folder name as an argument but I don't seem to get the regular expression right afer that.

You can use find to do this, see the example below. The -exec option in find uses {} to replace the name of the file here so in each instance {} is changed to {}.ext (here 1 to 1.ext, 2 to 2.ext etc

oeb@cloudnext:~/test$ touch 1 2 3 4 5 6
joeb@cloudnext:~/test$ find . -exec mv {} {}.ext \;
mv: cannot move `.' to `..ext': Device or resource busy
joeb@cloudnext:~/test$ ls -lsa
total 8
4 drwxr-xr-x 2 joeb joeb 4096 2010-03-26 13:36 .
4 drwxr-xr-x 5 joeb joeb 4096 2010-03-26 13:35 ..
0 -rw-r--r-- 1 joeb joeb 0 2010-03-26 13:35 1.ext
0 -rw-r--r-- 1 joeb joeb 0 2010-03-26 13:35 2.ext
0 -rw-r--r-- 1 joeb joeb 0 2010-03-26 13:35 3.ext
0 -rw-r--r-- 1 joeb joeb 0 2010-03-26 13:35 4.ext
0 -rw-r--r-- 1 joeb joeb 0 2010-03-26 13:35 5.ext
0 -rw-r--r-- 1 joeb joeb 0 2010-03-26 13:35 6.ext

Sigh. Sorry to be snarky, but...

Did you ever think about using the search function? There must be literally hundreds of threads asking this same or similar question. The post creation page you used even had a function that would do it automatically for you. Even now you can just look to the bottom of the page and follow some of the "similar threads".

Not to mention that there's always Google.

As a note, the find command will also do all sub file and directories unless you specify a depth, read the find man page for more details, maybe a more complete command would be:

find . -maxdepth 0 -type f -exec mv {} {}.ext \;