Matching within multiline strings, and ignoring case in regular expressions

Regular Expressions are powerful matching tools and you can specify almost anything within them. But there are certain facilities that are naturally applied to the regular expression as a whole rather than to parts of the match, and there are specified in a different way in each language / implementation.

For example, in what is commonly known as multiline mode you may want to match not only at the start / end of the string as a whole, but also match at embedded new lines. You can specify multiline mode as follows:

In Tcl, using the -lineanchor option
In Perl, with the /m modifier on the end of your regex
In Python by adding re.M or re.MULTILINE to your compile

Here's an example, in Tcl, looking for embedded lined containing just ABC:

set samples [list "Hello world\nABC\nThis matches" \

        "Another test\nABCD\nNo match" ]



foreach sample $samples {

        puts [regexp -lineanchor {^ABC$} $sample]

        }

ther facilities often added onto your regular expression as modifiers include:

a) The ability to have "." (the dot) match any character at all, and not to exclude the newline character which it does by default. Sometimes known as single line of linestop mode.

In Tcl, leave off the -linestop option
In Perl, add /s
In python, add re.DOTALL onto the compile

b) The ability to ignore case in the match

In Perl, /i
In Python, re.I or re.IGNORECASE
In Tcl, use (?i through ) in the regex

c) The ability to add white space as comments into your expression

In Perl, /x
In Python, re.VERBOSE
In Tcl, use (?X through ) in the regex
(written 2006-11-25, updated 2006-11-26)

Associated topics are indexed under

P212 - Perl - More on Character Strings
  [3927] First match or all matches? Perl Regular Expressions - (2012-11-19)
  [3707] Converting codons via Amino Acids to Proteins in Perl - (2012-04-25)
  [3650] Possessive Regular Expression Matching - Perl, Objective C and some other languages - (2012-03-12)
  [3630] Serialsing and unserialising data for storage and transfer in Perl - (2012-02-28)
  [3546] The difference between dot (a.k.a. full stop, period) and comma in Perl - (2011-12-09)
  [3411] Single and double quotes strings in Perl - what is the difference? - (2011-08-30)
  [3332] DNA to Amino Acid - a sample Perl script - (2011-06-24)
  [3322] How much has Perl (and other languages) changed? - (2011-06-10)
  [3100] Looking ahead and behind in Regular Expressions - double matching - (2010-12-23)
  [3059] Object Orientation in an hour and other Perl Lectures - (2010-11-18)
  [2993] Arrays v Lists - what is the difference, why use one or the other - (2010-10-10)
  [2877] Further more advanced Perl examples - (2010-07-19)
  [2874] Unpacking a Perl string into a list - (2010-07-16)
  [2834] Teaching examples in Perl - third and final part - (2010-06-27)
  [2801] Binary data handling with unpack in Perl - (2010-06-10)
  [2657] Want to do a big batch edit? Nothing beats Perl! - (2010-03-01)
  [2379] Making variables persistant, pretending a database is a variable and other Perl tricks - (2009-08-27)
  [2230] Running a piece of code is like drinking a pint of beer - (2009-06-11)
  [1947] Perl substitute - the e modifier - (2008-12-16)
  [1735] Finding words and work boundaries (MySQL, Perl, PHP) - (2008-08-03)
  [1727] Equality and looks like tests - Perl - (2008-07-29)
  [1510] Handling Binary data (.gif file example) in Perl - (2008-01-17)
  [1336] Ignore case in Regular Expression - (2007-09-08)
  [1305] Regular expressions made easy - building from components - (2007-08-16)
  [1251] Substitute operator / modifiers in Perl - (2007-06-28)
  [1230] Commenting a Perl Regular Expression - (2007-06-12)
  [1222] Perl, the substitute operator s - (2007-06-08)
  [928] C++ and Perl - why did they do it THAT way? - (2006-11-16)
  [737] Coloured text in a terminal from Perl - (2006-05-29)
  [608] Don't expose your regular expressions - (2006-02-15)
  [597] Storing a regular expression in a perl variable - (2006-02-09)
  [586] Perl Regular Expressions - finding the position and length of the match - (2006-02-02)
  [583] Remember to process blank lines - (2006-01-31)
  [453] Commenting Perl regular expressions - (2005-09-30)

Q803 - Object Orientation and General technical topics - Regular Expressions - Extra Elements
  [3516] Regular Expression modifiers in PHP - summary table - (2011-11-12)
  [3089] Python regular expressions - repeating, splitting, lookahead and lookbehind - (2010-12-17)
  [2909] Be gentle rather than macho ... regular expression techniques - (2010-08-08)
  [1860] Seven new intermediate Perl examples - (2008-10-30)
  [1613] Regular expression for 6 digits OR 25 digits - (2008-04-16)
  [1601] Replacing the last comma with an and - (2008-04-04)
  [1372] A taster PHP expression ... - (2007-09-30)

T205 - Tcl/Tk - String Handling in Tcl
  [3576] Tcl - apparently odd behaviour of string trimleft - (2012-01-13)
  [3285] Extracting data from a string / line from file - Tcl - (2011-05-10)
  [3192] Tcl - Some example of HOW TO in handling data files and formats - (2011-03-04)
  [2472] split and join in tcl and expect - (2009-10-23)
  [1410] Tcl / regsub - changing a string and using interesting bits - (2007-10-27)
  [1403] Square Bracket protection in Tcl - (2007-10-23)
  [779] The fragility of pancakes - and better structures - (2006-06-26)
  [404] How to check that a string contains a number in Tcl - (2005-08-06)

T247 - Tcl/Tk - Advanced Regular Expressions
  [1412] Sparse and Greedy matching - Tcl 8.4 - (2007-10-27)
  [1195] Regular Express Primer - (2007-05-20)

Y108 - Python - String Handling
  [4027] Collections in Python - list tuple dict and string. - (2013-03-04)
  [3886] Formatting output - why we need to, and first Python example - (2012-10-09)
  [3796] Backquote, backtic, str and repr in Python - conversion object to string - (2012-07-05)
  [3469] Teaching dilemma - old tricks and techniques, or recent enhancements? - (2011-10-08)
  [3468] Python string formatting - the move from % to str.format - (2011-10-08)
  [3349] Formatting output in Python through str.format - (2011-07-07)
  [3218] Matching a license plate or product code - Regular Expressions - (2011-03-28)
  [3090] Matching to a string - what if it matches in many possible ways? - (2010-12-17)
  [2814] Python - splitting and joining strings - (2010-06-16)
  [2780] Formatted Printing in Python - (2010-05-25)
  [2765] Running operating system commands from your Python program - (2010-05-14)
  [2721] Regular Expressions in Python - (2010-04-14)
  [2692] Flexible search and replace in Python - (2010-03-25)
  [2406] Pound Sign in Python Program - (2009-09-15)
  [2284] Strings as collections in Python - (2009-07-12)
  [1876] Python Regular Expressions - (2008-11-08)
  [1608] Underlining in Perl and Python - the x and * operator in use - (2008-04-12)
  [1517] Python - formatting objects - (2008-01-24)
  [1110] Python - two different splits - (2007-03-15)
  [970] String duplication - x in Perl, * in Python and Ruby - (2006-12-07)
  [954] Splitting Pythons in Bradford - (2006-11-29)
  [903] Pieces of Python - (2006-10-23)
  [773] Breaking bread - (2006-06-22)
  [560] The fencepost problem - (2006-01-10)
  [496] Python printf - (2005-11-15)
  [463] Splitting the difference - (2005-10-13)
  [324] The backtick operator in Python and Perl - (2005-05-25)

4ad9

Back to
Index of Pictures

Previous and next
or
Horse's mouth home

Forward to
Just ******* Google it

Some other Articles

What is an SQL injection attack?
Look around this mouth.
Code quality counts
Just ******* Google it
Matching within multiline strings, and ignoring case in regular expressions
Index of Pictures
Snagging
Winter at Well House Manor - Open Houses
Swipe cards for hotel rooms - Security issues
Bratton and Edington new town, Wiltshire

4084 posts, page by page

Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82 at 50 posts per page

This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

Link to Ezine home page (for reading).
Link to Blogging home page (to add comments).

You can Add a comment or ranking to this page

Public Training Courses

Running regularly at our UK training Centre.
[Schedule] - [About] - [Book]

Like this? ??