Change file's numbers Bash

Question

I need to implement a script (duplq.sh) that would rename all the text files existing in the current directory using the command line arguments. So if the command duplq.sh

Answer 1

A possible solution...

#!/bin/sh

NUMBERS=$(ls $1|sed -e 's/pic//g' -e 's/\.txt//g'|sort -n -r)

for N in $NUMBERS
do
    NEW=$(($N + 3))
    echo "pic$N.txt -> pic$NEW.txt"
    mv "pic$N.txt" "pic$NEW.txt"
done

Answer 2

find possible files, sort the names by number, use sed to remove files with lower numbers than $1, reverse sort by number, and start at the top renaming from the highest number down to the lowest:

#!/bin/sh
find . -maxdepth 1 -type f -name "$1"'[0-9]*' | 
sort -g | sed -n "/^$1$2."'/,$p' | sort -gr | 
while read x ; do
    p="${x%%[0-9]*.*}"; s="${x##*[0-9]}" ; i="${x%$s}" i="${i#$p}"
    mv "$x" "$p$((i+$3))$s"
done