Re-index files by changing the index suffix of file names.

reindex_files.sh

#!/bin/bash
# Re-index files by changing the index suffix of file names.
# Usage: reindex_files <pattern> <offset>
# It renames all files in the folder following "pattern + number + extension" naming.
# <pattern> can be any regex (care not to match the index number).
# <number> is an integer ([0-9]+)
# It works for files with no extension as well.
# It will ask for confirmation before renaming the files.
rename_all(){

  pattern=$1
  offset=$2
  apply=$3

  for filename in *; do

    if [[ "$filename" =~ ^${pattern}.* ]]; then

      extension=".${filename##*.}"
      basename="${filename%.*}"

      # no extension?
      if [[ "$extension" == ".$basename" ]]; then
        extension=""
      fi

      # get the index and prefix
      [[ $basename =~ (^${pattern})([0-9]+) ]]
      prefix=${BASH_REMATCH[1]}
      old_index=${BASH_REMATCH[2]}

      index=$((old_index + offset))

      echo "$filename > $prefix$index$extension"
      if [[ $apply = "y" ]]; then
        mv "$filename" "$prefix$index$extension"
      fi
    fi
  done
}

if [ "$#" -ne "2" ]; then
  echo "Usage: reindex_files <prefix> <offset>"
  echo "prefix can be a regex expression"
  exit 0
fi

rename_all $1 $2 "n"

read -p "Above changes are ok? (y/n)" yn
# user consent
if [ "$yn" == "y" ]; then

  rename_all $1 $2 "y"
  echo "renamed files"
fi

echo "finished"