Shell Programming and Scripting

ls a_*.out > file_list
awk -F"[_.]" '{print $2" "$0}' file_list|sort -n|awk '{print $2}' > temp
mv temp > file_list
while read f
do
 awk <your-program> "$f"
done < file_list

ls a_*.out | sort -t_ -k2n |
while read f
do 
  awk... "$f"
done

$ awk '{arr[$1]=arr[$1] " " $2}END{for(i in arr)print i,arr[i]}' file1 file2 etc

ls a_*.out | sort -t_ -k2n |
while read f
do 
  cat "$f"
done |
awk '{arr[$1]=arr[$1] " " $2}END{for(i in arr)print i,arr[i]}'

awk '{arr[$1]=arr[$1] " " $2}END{for(i in arr)print i,arr[i]}' `ls a_*.out | sort -t_ -k2n`