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lanx@lanx-1005HA:~$ perl -MO=Terse -e 's/(x)/$1.$1/re' LISTOP (0x8eb6668) leave [1] ... PADOP (0x8ebfe20) gvsv GV (0x8ef1c90) *1 UNOP (0x8ebfc98) null [15] PADOP (0x8ebfcb8) gvsv GV (0x8ef1c90) *1
lanx@lanx-1005HA:~$ perl -e 'sub bla { s/x/BEGIN{print "compiletime\n" +}/e }' compiletime