Don't we all get through this one every so often? exploring some other possibilities ..

perl -le 'print $1 while ($ARGV[0] =~ s/(.{1,2})(.*)/$2/g);' "12345678
+9"

perl -le '$c=-2; print while $_ = substr $ARGV[0], $c+=2, 2;' "1234567
+89"
# or
perl -le 'while ($_ = substr $ARGV[0], $c, 2) { print; $c+=2 };' "1234
+56789"

perl -le '@_=reverse split//, $ARGV[0]; while (@_) {print join"", (pop
+@_, pop@_);}' "123456789"

perl -le '@_=split//, $ARGV[0]; while (@_) {print join"", (shift@_, sh
+ift@_);}' "123456789"

perl -le '@_=split//, $ARGV[0]; while (@_) {print join "", splice @_, 
+0, 2}' "123456789"

perl -le '@_ = split //,$ARGV[0]; splice @_, $_, 2, $_[$_].$_[$_+1] fo
+r 0..$#_/2; print "@_"' "123456789"

# some alternatives to ones already posted..
 perl -le 'print for grep /./, split /(..)/, $ARGV[0]' "123456789"

perl -le 'print for unpack "(Z2)*", $ARGV[0]' "123456789"

# probably the fastest
echo 123456789 | perl -nle 'print for /(..?)/g'
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