Regular Expressions in PHP

Nov 4, 2011Download as PPTX, PDF2 likes3,937 views

From my November 3, 2011 talk at MNPHP. Regular expressions are a powerful tool available in nearly every programming language or platform, including PHP. I go over the history of POSIX vs. PCRE, examples in PHP, and optimizations on how to write faster expressions.

Regular Expressions for the
Web Application Developer
By Andrew Kandels

Regular Expressions
Regular expressions provide a concise, flexible means for
matching strings of text, such as words or patterns of
characters.
POSIX PCRE
Portable Operating System Interface Perl Compatible Regular Expressions

• Traditional Unix regular • Perl 5 Extended Features
expression syntax • Native C Extension
• Generally Faster
• PHP’s ereg_ functions • Optimization Qualifiers

• Basic and extended versions Used by:
• Programming languages
• Apache and other servers

Why Use Them?
• Input Validation
• Input Filtering
• Search and Replace
• Parsing and Data Extraction
• Dynamic Recursion
• Automation

In PHP, POSIX = Deprecated
ereg_* functions are now deprecated in newer versions of
PHP.
Switching to preg_* is generally pain free. Pain points:

• Different matching criteria (greed)
• preg_* requires delimiters
• Different characters require escape sequences
• preg favors option modifiers over functions

Anatomy of a PHP Regular Expression

/foo/i
• Delimiters
• Pattern to match
• Options/modifiers
preg_replace(
„/(href|src)=„([^‟])*‟/i‟,
„1=“2”‟,
$str
);

PHP Regular Expressions

• Must use a delimiter: ! @ # /
• Use PHP’s single quotes (no escaping ’s)

preg_match Match against a pattern and
extract text
preg_replace Like str_replace with a pattern
(and sub-patterns)
preg_match_all Like preg_match, but an array
and count for every match
preg_split Like explode() but with a
pattern
preg_quote Escapes text for use in a regular
expression

Modifiers and Options
i PCRE_CASELESS – Ignores case

m PCRE_MULTILINE – Ignores new-lines

s PCRE_DOTALL – New lines count with dots
(.)
U Don’t be greedy

Performance Killers

Slow-downs in performance generally come from:

• Alternation, the pipe/OR operator (|)
Use [abcd] when possible over (a|b|c|d)
• Multi-line (PCRE_DOTALL or /s)
• Recursion: (d+)d*
Use lengths when possible

It’s not that slow!

Sub-Patterns

Sub-Patterns allow you to extract relevant text from searches:

• For preg_replace, use either 1 or $1 in your replacement string
• Sub-patterns are left-most indexed by first left parenthesis “(“

Lookaheads
Are zero-match so they won’t modify your cursor or be included in any sub-patterns.

(?=pattern)
Pattern can be any valid regex

Lookbehinds

(?<!pattern)
Accepts some basic regex

Multi-Line Processing

/msU
(Multi-line, include newlines with dots, non-greedy)

Once-Only Sub-Patterns

Eliminates slow recursion from wildcard searching.

Less scans = more speed.

Greedy

By default, PCRE returns the biggest match.

100,000 runs took 0.2791 seconds

Non-Greedy with Modifier

The /U modifier returns the SMALLEST match.

100,000 runs took 0.2638 seconds
(a little better, and it’s right)

Restrictive Wild-Carding

No greedy flag needed, faster without broad wild-cards.

100,000 runs took 0.2271 seconds
(fastest yet, no options needed)

grep

Use grep –E or egrep for extended regular expressions (+, ?, |)
and advanced functionality.

-A n Print the next n lines after each match.
-B n Print the previous n lines before each match.
-i Ignore case
-m n Stop after n matches
-r Recursively search the file system
-n Show line numbers
-v Only show lines that don’t match

sed

Use –r (-E on OS X / FreeBSD) for extended regular expressions.

The End

Web: http://andrewkandels.com

Mail: mailto:akandels@gmail.com

Twitter: @andrewkandels

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Regular Expressions in PHP

1. Regular Expressions for the Web Application Developer By Andrew Kandels

2. Regular Expressions Regular expressions provide a concise, flexible means for matching strings of text, such as words or patterns of characters. POSIX PCRE Portable Operating System Interface Perl Compatible Regular Expressions • Traditional Unix regular • Perl 5 Extended Features expression syntax • Native C Extension • Generally Faster • PHP’s ereg_ functions • Optimization Qualifiers • Basic and extended versions Used by: • Programming languages • Apache and other servers

3. Why Use Them? • Input Validation • Input Filtering • Search and Replace • Parsing and Data Extraction • Dynamic Recursion • Automation

4. In PHP, POSIX = Deprecated ereg_* functions are now deprecated in newer versions of PHP. Switching to preg_* is generally pain free. Pain points: • Different matching criteria (greed) • preg_* requires delimiters • Different characters require escape sequences • preg favors option modifiers over functions

5. Anatomy of a PHP Regular Expression /foo/i • Delimiters • Pattern to match • Options/modifiers preg_replace( „/(href|src)=„([^‟])*‟/i‟, „1=“2”‟, $str );

6. PHP Regular Expressions • Must use a delimiter: ! @ # / • Use PHP’s single quotes (no escaping ’s) preg_match Match against a pattern and extract text preg_replace Like str_replace with a pattern (and sub-patterns) preg_match_all Like preg_match, but an array and count for every match preg_split Like explode() but with a pattern preg_quote Escapes text for use in a regular expression

7. Modifiers and Options i PCRE_CASELESS – Ignores case m PCRE_MULTILINE – Ignores new-lines s PCRE_DOTALL – New lines count with dots (.) U Don’t be greedy

8. Performance Killers Slow-downs in performance generally come from: • Alternation, the pipe/OR operator (|) Use [abcd] when possible over (a|b|c|d) • Multi-line (PCRE_DOTALL or /s) • Recursion: (d+)d* Use lengths when possible It’s not that slow!

9. Sub-Patterns Sub-Patterns allow you to extract relevant text from searches: • For preg_replace, use either 1 or $1 in your replacement string • Sub-patterns are left-most indexed by first left parenthesis “(“

10. Named Sub-Patterns (?P<name>pattern)

11. Lookaheads Are zero-match so they won’t modify your cursor or be included in any sub-patterns. (?=pattern) Pattern can be any valid regex

12. Lookbehinds (?<!pattern) Accepts some basic regex

13. Multi-Line Processing /msU (Multi-line, include newlines with dots, non-greedy)

14. Once-Only Sub-Patterns Eliminates slow recursion from wildcard searching. Less scans = more speed.

15. Greedy By default, PCRE returns the biggest match. 100,000 runs took 0.2791 seconds

16. Non-Greedy with Modifier The /U modifier returns the SMALLEST match. 100,000 runs took 0.2638 seconds (a little better, and it’s right)

17. Restrictive Wild-Carding No greedy flag needed, faster without broad wild-cards. 100,000 runs took 0.2271 seconds (fastest yet, no options needed)

18. grep Use grep –E or egrep for extended regular expressions (+, ?, |) and advanced functionality. -A n Print the next n lines after each match. -B n Print the previous n lines before each match. -i Ignore case -m n Stop after n matches -r Recursively search the file system -n Show line numbers -v Only show lines that don’t match

19. sed Use –r (-E on OS X / FreeBSD) for extended regular expressions.

20. The End Web: http://andrewkandels.com Mail: mailto:[email protected] Twitter: @andrewkandels

Regular Expressions in PHP

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Regular Expressions in PHP