Miscellaneous: Regual expressions
(last edit: 2000-11-22)
                   /abc/              is regual expression for: grep abc somefile
m#/usr/etc#        using # for a delimiter equal to /\/usr\/etc/

open(IN, "<somefile") || [exit the script]

while(<IN>) {
 if(/abc/) {
   print $_;
 }  
}

[abcde]            matches a or b or c or d or e
[0-9]              matches 0 or 1 or 2 ... or 9
[0-9\-]            matches 0-9 or minus
[a-z0-9]           matches any single lowercase letter or digit
[^0-9]             matches any single non-digit
[^\^]              matches single characters except an up-arrow
bla|bli            matches or 'bla' or 'bli'

\d                 a digit
\D                 not a digit
\w                 word
\W                 not a word
\s                 space
\S                 not a space
\b                 word boundary
\B                 no word boundary

/fred\b/           matches 'fred' but not 'frederick'
/\bmo/             matches 'moe', 'mole' but not 'elmo'
/\bFred\B/         matches 'Frederick' but not 'fred flinstone'

.                  any single non-newline character  
*                  zero of more
+                  one or more
?                  zero or one

^                  beginning of string
$                  end of string

^a                 matches an 'a' if and only if the 'a' is the first charcter of the string
a^                 ^ looses its meaning and this expression matches 'a' and '^'
$a                 see ^a
a$                 see a^

x{5,10}            five to ten x's
x{5,}              five or more x's
x{5}               five x's
x{0,5}             five or less x's
 
()                 grouping operator, causes the part of the string matchedc by the parrern to be remebered.

/fred(.)barney\1/  matches a strin consisting of fred, followd by any single non-newline character
                   followed by barney, followed by that smae singe character

/fred(.)barney/
print $1           prints the single non-newline character found by the '.' operator

/fred(.)barney(.)wilma\1\2/

print $1
print $2

s/abc/def/         substitutes 'abc' for 'def'
s/abc/i            ignores case
s/abc/g            substitutes all possible matches in string 
s#abc#def#         same as s/abc/def/ use this if th '/' is in the string you like to alter


Grouping precedence
Parantheses        ( ) (?: )
Multipliers        ? + * {m,n} ?? +? *? {m,n}?
Sequence and
anchoring          abc ^ $ \A \Z (?= ) (?! )
Alternation        |