Ubuntu – Rename files with one line command

As an alternative to the various Perl-based methods in other answers, you can do this particular example, and lots of other similar ones with plain bash:

for i in randomized_quad???.png; do   
  mv $i randomized_quad0${i#randomized_quad}
done

This loops over the filenames with only three characters in the number region, and the variable expression in braces takes each filename, snips "randomized_quad" off the front (with the # operator), and adds "randomized_quad0" on the front.

Other excitingly useful operators like this include:

• % - cut something off the end
• / - search and replace (/ for the first match, // for all matches)
• : - for extracting substrings

A more complete list with examples is here. Also, note that these use POSIX-style regular expressions, so . will match any character, not just a "." If you want to match a ".", you should 'escape' it, with a backslash:

TestVariable1="filename.png"
TestVariable2="filename0png"

echo "${TestVariable1%.png}"
> filename

echo "${TestVariable2%.png}"
> filename

echo "${TestVariable1%\.png}"
> filename

echo "${TestVariable2%\.png}"
> filename0png

You can use the rename command, which is usually included in a default installation:

rename 's/.*/sprintf("filename (%d)", ++$ENV{c})/e' *

This would do precisely what you asked for. Use the -n flag if you want to do a test first:

rename -n 's/.*/sprintf("filename (%d)", ++$ENV{c})/e' *

This assumes that the environment variable c is undefined, which will cause the count to start from 0. If you want to be extra safe, you could call it like this:

c=0 rename -n 's/.*/sprintf("filename (%d)", ++$ENV{c})/e' *