find the position in 1st file where its binary match the head of 2nd file, and begin cmp at that position; Usage: $ . index_cmp.sh file1 file2 [offset_of_file2_head(default_0) [length_of_file2_head_to_search(default_1000) [offset_in_file1_to_start_search(default_0)]]]

eval_1.sh

#set -- "$@"
#. /dev/null
if : || [[ "$1" != "set "* ]] ; then
#echo '$ '
#echo "$1" ; eval "$1"
echo '$ ' >&2
#echo "$1" >&2 ; eval "$1"
#echo "$1" >&2 ; eval "shift ; . /dev/null ; $1"
# * sourcing make it not return $@, but no this effect when shift
#echo "$1" >&2 ; eval 'shift ; (( $# > 0 )) && set -- "$@" ; '"$1"
echo "$1" >&2 ; if (( $# > 1 )) ; then eval 'shift ; '"$1" ; set -- "$@"
                                  else eval 'shift ; '"$1" ; fi
#. /dev/null
else
   echo '$ ' >&2
   echo "$1" >&2 ; eval "$1"
fi

index_cmp.sh

# $ { head -1000c /home/sysadmin/tmp/f139.3 ; cat /home/sysadmin/tmp/f139.2 ; } | perl -le 'read(STDIN, $a, 1000); print index(join("",<STDIN>),$a)+1'
#{ head -1000c "$2" ; cat "$1" ; } | perl -le 'read(STDIN, $a, 1000); print index(join("",<STDIN>),$a)+1'
#set -- "$1" "$2" "`{ head -1000c "$2" ; cat "$1" ; } | perl -le 'read(STDIN, $a, 1000); print index(join("",<STDIN>),$a)+1'`"
#set -- "$1" "$2" "`perl -le 'open(F, "<", $ARGV[0]); read(F, $a, 1000); close(F); print index(join("",<STDIN>),$a)+1' "$2" < "$1"`"
#set -- "$1" "$2" `perl -le 'open(F, "<", $ARGV[0]); read(F, $a, 1000); close(F); read(STDIN,$b,2000000); for($o=0;;){ read(STDIN,$c,2000000); $i=index($b.substr($c,0,1000-1),$a); if($i>=0){print $o+$i+1;last;} if($c eq""){last;} $o+=length$b; $b=$c; }' "$2" < "$1"`
#. /dev/null
#while (( $# > 2 )) ; do
#   (( "$3" > 0 )) && {
#   #tail -c+"$3" "$1" | cmp "$2"
#   #tail -c+"$3" "$1" | wc -c
#   #. eval_1.sh "tail -c+$3 $1 | cmp $2"
#   #. eval_1.sh "tail -c+$3 $1 | wc -c"
#   . eval_1.sh "tail -c+$3 $1 | cmp $2" 2>&1| tee /dev/stderr | grep --color=always -Fx 'cmp: EOF on -'
#   . eval_1.sh "tail -c+$3 $1 | wc -c" 2>&1| tee /dev/stderr | grep --color=always -Fx 0
#   }
#set -- "$1" "$2" "${@:4}"; . /dev/null ; done

#set -- "$1" "$2" "$3" `perl -le 'open(F, "<", $ARGV[0]); seek(F,$ARGV[1],0); read(F,$a,1000); close(F); read(STDIN,$b,2000000); for($o=0;;){ read(STDIN,$c,2000000); $i=index($b.substr($c,0,1000-1),$a); if($i>=0){print $o+$i+1;last;} if($c eq""){last;} $o+=length$b; $b=$c; }' "$2" "$3" < "$1"`
#set -- "$1" "$2" "$3" `perl -le 'open(F, "<", $ARGV[0]); seek(F,$ARGV[1],0); BEGIN{scalar@ARGV<3 and $ARGV[2]=1000} read(F,$a,$ARGV[2]); close(F); read(STDIN,$b,2000000); for($o=0;;){ read(STDIN,$c,2000000); $i=index($b.substr($c,0,$ARGV[2]-1),$a); if($i>=0){print $o+$i+1;last;} if($c eq""){last;} $o+=length$b; $b=$c; }' "$2" "$3" "${@:4}" < "$1"`
#set -- "$1" "$2" "$3" `perl -le 'open(F, "<", $ARGV[0]); seek(F,$ARGV[1]+0,0); BEGIN{scalar@ARGV<3 and $ARGV[2]=1000} read(F,$a,$ARGV[2]); close(F); read(STDIN,$b,2000000); for($o=0;;){ read(STDIN,$c,2000000); $i=index($b.substr($c,0,$ARGV[2]-1),$a); if($i>=0){print $o+$i+1;last;} if($c eq""){last;} $o+=length$b; $b=$c; }' "$2" "$3" "${@:4}" < "$1"`
set -- "$1" "$2" "$3" `perl -le 'open(F, "<", $ARGV[0]); seek(F,$ARGV[1]+0,0); BEGIN{scalar@ARGV<3 and $ARGV[2]=1000; scalar@ARGV<4 and $ARGV[3]=0; } read(F,$a,$ARGV[2]); close(F); seek(STDIN,$ARGV[3]+0,0); read(STDIN,$b,2000000); for($o=0;;){ read(STDIN,$c,2000000); $i=index($b.substr($c,0,$ARGV[2]-1),$a); if($i>=0){print $ARGV[3]+$o+$i+1;last;} if($c eq""){last;} $o+=length$b; $b=$c; }' "$2" "$3" "${@:4}" < "$1"`
. /dev/null
# * escape file name
set -- "$1" "$2" "'\''" "${@:3}"
set -- \'"${1//\'/$3}"\' \'"${2//\'/$3}"\' "${@:4}"
. /dev/null
while (( $# >= 4 )) ; do
   (( "$4" > 0 )) && {
   #tail -c+"$4" "$1" | cmp "$2"
   #tail -c+"$4" "$1" | wc -c
   #. eval_1.sh "tail -c+$4 $1 | cmp $2"
   #. eval_1.sh "tail -c+$4 $1 | wc -c"
   #if [[ "$3" == "" ]] ; then
   if [[ "$3" == "" ]] || (( "$3" == 0 )) ; then
   #. eval_1.sh "tail -c +$4 $1 | cmp $2" 2>&1| tee /dev/stderr | grep --color=always -Fx 'cmp: EOF on -'
   #. eval_1.sh "tail -c +$4 $1 | wc -c" 2>&1| tee /dev/stderr | grep --color=always -Fx 0
   #. eval_1.sh "tail -c +$4 -- $1 | cmp -- $2" 2>&1| tee /dev/stderr | grep --color=always -Fx 'cmp: EOF on -'
   #. eval_1.sh "cmp -i "$(($4-1))":0 -- $1 $2" 2>&1| tee /dev/stderr | eval grep --color=always -Fx "'cmp: EOF on '$1"
   . eval_1.sh "cmp -i $(($4-1)):0 -- $1 $2" 2>&1| tee /dev/stderr | eval grep --color=always -Fx "'cmp: EOF on '$1"
   . eval_1.sh "tail -c +$4 -- $1 | wc -c" 2>&1| tee /dev/stderr | grep --color=always -Fx 0
   else
   #. eval_1.sh "{ head -c $3 $2 ; tail -c +$4 $1 ; } | cmp $2" 2>&1| tee /dev/stderr | grep --color=always -Fx 'cmp: EOF on -'
   ##. eval_1.sh "{ head -c $3 $2 ; tail -c +$4 $1 ; } | wc -c" 2>&1| tee /dev/stderr | grep --color=always -Fx 0
   #. eval_1.sh "tail -c +$4 $1 | wc -c" 2>&1| tee /dev/stderr | grep --color=always -Fx 0
   #. eval_1.sh "{ head -c $3 -- $2 ; tail -c +$4 -- $1 ; } | cmp -- $2" 2>&1| tee /dev/stderr | grep --color=always -Fx 'cmp: EOF on -'
   #. eval_1.sh "cmp -i "$(($4-1))":$3 -- $1 $2" 2>&1| tee /dev/stderr | eval grep --color=always -Fx "'cmp: EOF on '$1"
   . eval_1.sh "cmp -i $(($4-1)):$3 -- $1 $2" 2>&1| tee /dev/stderr | eval grep --color=always -Fx "'cmp: EOF on '$1"
   #. eval_1.sh "{ head -c $3 -- $2 ; tail -c +$4 -- $1 ; } | wc -c" 2>&1| tee /dev/stderr | grep --color=always -Fx 0
   . eval_1.sh "tail -c +$4 -- $1 | wc -c" 2>&1| tee /dev/stderr | grep --color=always -Fx 0
   fi
   }
set -- "$1" "$2" "$3" "${@:5}" ; . /dev/null ; done

Usage: $ . index_cmp.sh file1 file2 [offset_of_file2_head(default_0) [length_of_file2_head_to_search(default_1000) [offset_in_file1_to_start_search(default_0)]]]

Example: $ . index_cmp.sh file1 file2

Example: $ . index_cmp.sh file1 file2 0 188