$ perl -le'$x = "hexadecimal addr:0xdf7780 value"; print $x; $x =~ s/ addr:0x \K ( [[:xdigit:]]+ ) / $y = "500000000"; $l = length $1; substr $y, -$l, $l, $1; $y /xe; print $x' hexadecimal addr:0xdf7780 value hexadecimal addr:0x500df7780 value