grep searches a file for a given pattern
Execute by
   grep [flags] regular_expr file_list

Flags are single chars preceeded by '-':
 -c   Only a count of matching lines
       is printed
 -f   Print file name for matching 
       lines switch, see below
 -n   Each line is preceeded by its
       line number
 -v   Only print non-matching lines

The file_list is a list of files 


The file name is normally printed if 
there is a file given.
The -f flag reverses this action 
(print name no file, not if more).

The regular_expression defines the pat-
tern to search for.  Upper- and lower-
case are always ignored.  Blank lines 
never match.  The expression should be 
quoted to prevent filename translation

x    An ordinary character 
     (not mentioned below) matches
     that character.

'\'  The backslash quotes any char.
"\$" matches a dollar-sign.

'^'  A circumflex at the beginning of
     expression matches the beginning 
     of a line.

'$'  A dollar-sign at the end of an 
    expr matches the end of a line

'.'  A period matches any character 
     except "new-line".

':a'  A colon matches a class of chars 
      described by the following
':d'  character.  ":a" matches any 
      alphabetic, ":d" matches digits,
':n'  ":n" matches alphanumerics, 

": "  matches spaces, tabs, and
': '     other control characters, 
      such as new-line.

'*'   An expression followed by an 
      asterisk matches zero or more
      occurrances of that expression:
"fo*" matches "f", "fo" "foo", etc.

'+'   An expression followed by a plus
      sign matches one or more
      occurrances of that expression:
"fo+" matches "fo", etc.

'-'   An expression followed by a minus
      sign optionally matches
      the expression.

'[]'   A string enclosed in square 
       brackets matches any character
    in that string, but no others.
    If the first char in the string is a 
    circumflex, the expr matches any 
    char except "new-line" and the chars
    in the string.  For example, "[xyz]"
    matches "xx" and "zyx",while "[^xyz]"
    matches "abc" but not "axb".  
    A range of chars may be specified
    by two characters separated by "-".
    Note that, [a-z] matches alphabetics,
    while [z-a] never matches.
    The concatenation of regular 
    expressions is a regular expression.