Make a new directory and name the directory whatever name you choose. Change directories with cd to the new directory that you made, so that all of the files that are created by the shell script will be created inside the new directory and only these newly created files will be renamed. Then run the following shell script.

#!/bin/bash

for i in $(seq 1 100)

do

echo $RANDOM > ${i}.txt # Put a random number inside each file.

mv ${i}.txt $(head -1 ${i}.txt).txt # Rename the files.

done

ls *.txt | sort -n # Sort the files in ascending order.

Your question is ambiguous because I could also rename the files in ascending order with new names that range from 1.txt to 100.txt.
If that's how your want the files to be renamed use this shell script instead.

#!/bin/bash

for i in $(seq 1 100)

do

echo $RANDOM > ${i}.txt # put a random number inside each file

mv ${i}.txt $(head -1 ${i}.txt).txt # rename files

done

# ls *.txt | sort -n # I commented out this line and added a new line after it.

i=1; for filename in `ls *.txt | sort -n`; do mv "$filename" "$((i++)).txt"; done