Ubuntu – How to batch rename files with terminal

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

constant=42
for f in *.txt; do    # choose your pattern as appropriate.
    IFS='-.' read id suffix ext <<< "$f"
    newname="$(( 10#$id + constant ))-yyy.$ext"
    echo mv "$f" "$newname"
done

I added "10#" in the arithmetic expression to ensure the number is treated as base-10 even if it begins with a zero.

If this doesn't meet your needs, please provide more requirements in the question.