#!/bin/bash
SAVEIFS=$IFS
IFS=$(echo -en "\n\b")
for f in *1.wmv
do
  shortfile=${f::-5}
  echo "file '"$shortfile"1.wmv" > list.txt
  echo "file '"$shortfile"2.wmv" >> list.txt
  echo "file '"$shortfile"3.wmv" >> list.txt
  ffmpeg -f concat -safe 0 -i list.txt -c copy $shortfile.wmv
  rm list.txt
done
IFS=$SAVEIFS