Shell Programming and Scripting

# grep -v -f File1.txt File2.txt
keyx=valuex
#

These all assume there is nothing in the files except "key" 
lines that you are interested in. If not, this can be added 
to the first two commands: | grep "^key"

ls | while read file
   do grep -v -f File1.txt $file 
done 

or...

ls | xargs -n1 grep -v -f File1.txt 

or...

grep -v -f File1.txt $(ls)

or...

grep -v -f File1.txt *

$ cat file1.txt
key1=value1
key2=value2

$ cat file2.txt
key1=value1
key2=value2
key21=value21
key22=value22
key23=value23
key24=value24

$ cat file3.txt
key1=value1
key2=value2
key31=value31
key32=value32
key33=value33
key34=value34

$ cat file4.txt
key1=value1
key2=value2
key41=value41
key42=value42
key43=value43
key44=value44

#!/usr/bin/perl

my $datadir = "/home/mydir";
my $bfile = "file1.txt";
my %seen;
my $key;
my @flist;
my $keyfile;

open (BOILER_FILE, "<$bfile")
  or die "ERROR:  Unable to open $bfile";

while ($line = <BOILER_FILE>) {
   chomp $line;
   $key = ( split /=/, $line )[0];
   $seen{$key} = 1;

   print "BOILER KEY:  $key\n";
}

close (BOILER_FILE);

opendir DIRHANDLE, $datadir  or
   die "ERROR:  Unable to access $datadir" ;

@flist = (readdir(DIRHANDLE));
close DIRHANDLE;

for $keyfile (@flist) {

   next unless ($keyfile =~ /file.+\.txt/ && $keyfile ne $bfile);

   print "FILE:  $keyfile\n";

   open ( INFILE, "$datadir/$keyfile" )
      or die "ERROR:  Unable to open $keyfile";

   while ($line = <INFILE>) {
      chomp $line;
      $key = ( split /=/, $line )[0];

      next unless ! $seen{$key};

      print "   EXTRA KEY:  $key\n";
   }
}

exit 0

$ ./chk_keys.pl
BOILER KEY:  key1
BOILER KEY:  key2
FILE:  file2.txt
   EXTRA KEY:  key21
   EXTRA KEY:  key22
   EXTRA KEY:  key23
   EXTRA KEY:  key24
FILE:  file3.txt
   EXTRA KEY:  key31
   EXTRA KEY:  key32
   EXTRA KEY:  key33
   EXTRA KEY:  key34
FILE:  file4.txt
   EXTRA KEY:  key41
   EXTRA KEY:  key42
   EXTRA KEY:  key43
   EXTRA KEY:  key44

join -t= -v2 template data

[house@discovery] diff file1 file2
2a3
> keyx=valuex