regex - matching start of the line in cygwin regexp

I apply sed 's/^ bug*/__/' to

  ref      bug
  bug      ref

and get

  ref     __
 __      ref

The same is responded for perl, perl -ni -e 's/^ bug/__/; print'. Sample file can be downloaded from here. Sed and perl are cygwin utilities that I run from the Windows command line. When I run them through cygwin bash, this stuff does not happen.

Answer

The problem has to do with cmd.exe's "quirks" (for lack of a better word) with handling non-alphanumeric characters within single quotes in this case. Essentially, the caret and space characters are being ignored.

The easiest way to avoid the problem (if running it in a proper Cygwin bash shell is not a desirable option) would be to use double quotes instead...

C:\cygwin\home\costa\wk>sed 's/^  bug*/__/' sed.txt
  ref    __
__      ref

C:\cygwin\home\costa\wk>sed "s/^  bug*/__/" sed.txt
  ref      bug
__      ref