Shell Programming and Scripting

awk 'END { for (r in _) if (_[r] == ARGC - 1) print r }
{ _[$0]++ }' filename1 [filename2 .. ]

#!/usr/bin/env sh

# @(#) user2    Demonstrate finding lines in common.

#  ____
# /
# |   Infrastructure BEGIN

set -o nounset
echo

## The shebang using "env" line is designed for portability. For
#  higher security, use:
#
#  #!/bin/sh -

## Use local command version for the commands in this demonstration.

set +o nounset
echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version =o $(_eat $0 $1) awk
set -o nounset

for file in f*
do
  echo
  echo " -- $file --"
  cat -n $file
done

# Use nawk or /usr/xpg4/bin/awk on Solaris.

# |   Infrastructure END
# \
#  ---

echo
echo " Results from awk:"
filecnt=$( ls -1 f* | wc -l )

awk '
END     { for (r in _)
                if (_[r] == ARGC - 1)
                        print r
        }
        { _[$0]++ }
' f*

exit 0

% ./user2

(Versions displayed with local utility "version")
Linux 2.6.11-x1
GNU bash, version 2.05b.0(1)-release (i386-pc-linux-gnu)
GNU Awk 3.1.4

 -- f1 --
     1  a
     2  b
     3  x
     4  x

 -- f2 --
     1  a
     2  d
     3  y
     4  y

 Results from awk:
x
y
a

awk 'END { 
  for (r in __) 
    if (__[r] == ARGC -1) 
      print r 
  }
!_[FILENAME,$0]++ { 
  __[$0]++ 
  }' filename1 [fileaname2 .. filenamen]