PHP's
ereg functions are deprecated, and you should now be moving to the
preg functions. See
[here]. As you're switching your PHP code from
ereg to
preg regular expressions, you'll be adding delimiters to the main regular expression and providing the ability to add
modifiers onto the end - a series of single letters each of which alters a behaviour throughout the regular expression.
Perl users may be familiar with the following,
all of which are also available in PHP's preg functions:
i ignore case
m match ^ and $ at embedded new lines as well as very start and end of string
s matches anything (by default matches anything except \n)
x white spaces and comments (# to line end) are treated as comments
e preg_replace only. evaluate OUTPUT string as PHP code and substitute the result
In addition, PHP also supports the following modifiers:
A assume ^ anchor at start
D assume $ anchor at end
S Study; do more initial analysis for faster matching
U default counts to sparse (ungreedy). Extra ? becomes greedy (i.e. invert default)
X unknown \letter combination's are to throw an error not be ignored
J Allow duplicate names for sub-patterns
u treat patterns as UTF-8 rather than ASCII
However, these two perl modifiers are NOT available in PHP:
g global (use count instead on preg_replace, or use preg_match_all rather than preg_match)
o once only. An efficiency thing in Perl. No code change needed in PHP
The full technical reference that describes each of these in detail (but currently lacks my summary table!) is
[here]. We cover regular expressions in PHP on both our
earning to program in PHP and
PHP Programming courses. They are covered in more depth on our
PHP techniques course - a second level course which helps delegates who already know PHP make the best of the language, and we also offer a complete
Regular Expressions day.
(written 2011-11-12, updated 2011-11-27)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Q803 - Object Orientation and General technical topics - Regular Expressions - Extra Elements [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
[1336] Ignore case in Regular Expression - (2007-09-08)
[1372] A taster PHP expression ... - (2007-09-30)
[1601] Replacing the last comma with an and - (2008-04-04)
[1613] Regular expression for 6 digits OR 25 digits - (2008-04-16)
[1735] Finding words and work boundaries (MySQL, Perl, PHP) - (2008-08-03)
[1860] Seven new intermediate Perl examples - (2008-10-30)
[2909] Be gentle rather than macho ... regular expression techniques - (2010-08-08)
[3089] Python regular expressions - repeating, splitting, lookahead and lookbehind - (2010-12-17)
[3100] Looking ahead and behind in Regular Expressions - double matching - (2010-12-23)
[3650] Possessive Regular Expression Matching - Perl, Objective C and some other languages - (2012-03-12)
H107 - String Handling in PHP [31] Here documents - (2004-08-28)
[54] PHP and natural sorting - (2004-09-19)
[337] the array returned by preg_match_all - (2005-06-06)
[422] PHP Magic Quotes - (2005-08-22)
[463] Splitting the difference - (2005-10-13)
[493] Running a Perl script within a PHP page - (2005-11-12)
[558] Converting between acres and hectares - (2006-01-08)
[560] The fencepost problem - (2006-01-10)
[574] PHP - dividing a string up into pieces - (2006-01-23)
[589] Robust PHP user inputs - (2006-02-03)
[608] Don't expose your regular expressions - (2006-02-15)
[642] How similar are two words - (2006-03-11)
[716] Evaluating arithmetic expressions in configuration files - (2006-05-10)
[728] Looking ahead and behind in a Regular Expression - (2006-05-22)
[1008] Date conversion - PHP - (2006-12-26)
[1058] PHP Regular expression to extrtact link and text - (2007-01-31)
[1195] Regular Express Primer - (2007-05-20)
[1533] Short and sweet and sticky - PHP form input - (2008-02-06)
[1603] Do not SHOUT and do not whisper - (2008-04-06)
[1799] Regular Expressions in PHP - (2008-09-16)
[2046] Finding variations on a surname - (2009-02-17)
[2165] Making Regular Expressions easy to read and maintain - (2009-05-10)
[2238] Handling nasty characters - Perl, PHP, Python, Tcl, Lua - (2009-06-14)
[2629] Curly braces within double quoted strings in PHP - (2010-02-09)
[3020] Handling (expanding) tabs in PHP - (2010-10-29)
[3424] Divide 10000 by 17. Do you get 588.235294117647, 588.24 or 588? - Ruby and PHP - (2011-09-08)
[3515] PHP - moving from ereg to preg for regular expressions - (2011-11-11)
[3534] Learning to program in PHP - Regular Expression and Associative Array examples - (2011-12-01)
[3788] Getting more than a yes / no answer from a regular expression pattern match - (2012-06-30)
[3789] More than just matching with a regular expression in PHP - (2012-06-30)
[3790] Solution looking for a problem? Lookahead and Lookbehind - (2012-06-30)
[4071] Setting up strings in PHP - (2013-04-27)
[4072] Splitting the difference with PHP - (2013-04-27)
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