help me in grep

Shell Programming and Scripting
1

hi ,

i m not able to recognize why one is working while other is not.

  grep  "Hi How r u"       filename

        above is searching  the pattern and prints the output.


 but the following is not able to search the perticular line in grep


 a="Hi How r u"

 grep  $a    filename

plz help me.

2

grep "$a" filename