Shell Programming and Scripting

file1
key1 description of keyf1
key2 descf1
key5 key descriptionf1


file 2
key2 description of keyf2
key3 descf2
key4 key descriptionf2


file 3
key5 description of keyf3
key6 descf3
key7 key descriptionf3

file4 

key6 description of keyf4
key7 descf4
key8 key descriptionf4

output 
key1 description of keyf1 file1
key2 descf1 file1
key3 descf2 file2
key4 key descriptionf2 file2
key5 key descriptionf1 file1
key6 descf3 file3
key7 key descriptionf3 file3
key8 key descriptionf4 file4

grep "" file[1-4] | tr : ' ' | sort -k2,2 | awk -F" " '!L[$2]++ {$(NF+1)=$1; $1="";  print}'
 key1 description of keyf1 file1
 key2 descf1 file1
 key3 descf2 file2
 key4 key descriptionf2 file2
 key5 key descriptionf1 file1
 key6 descf3 file3
 key7 key descriptionf3 file3
 key8 key descriptionf4 file4

#!/bin/sh
awk '{ print $1 }' file? | sort | while read key
do
  greptuple=`grep "^$key " file? | head -1` 
  filename=`echo "$greptuple" | cut -d ':' -f 1`
  description=`echo "$greptuple" | sed 's/^[^ ]* //'`
  echo "$key $description $file"
done

awk '!a[$1]{x=$1;$1="";a[x]=$0" "FILENAME}END{for (i in a) print i,a[i]}' file1 file2 file3 file4

awk '!($1 in F) {F[$1]; R[++l]=$0 OFS FILENAME} END{for(i=1;i<=l;i++) print R[i]}' file*

awk '!a[$1]{a[$1]=$0" "FILENAME}END{for (i in a) print a[i]}' file1 file2 file3 file4