PHP and MySQL by Example- P11

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Figure 12.11. Splitting with multiple delimiters. Output from Example 12.10. Example 12.11. Explanation 1 This is the string that will be split up. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
2 By using an empty delimiter, preg_split() will split up the string by its individual characters. The PREG_SPLIT_NO_EMPTY flag causes the function to return an array without any empty elements. 3 The array of letters created by splitting on an empty delimiter is displayed as an array by the print_r() function, shown in Figure 12.12. Figure 12.12. Splitting up a word with the preg_split() function. Output from Example 12.11. Example 12.12.
2 $array=preg_split("/\s/", $alpha, -1, PREG_SPLIT_OFFSET_CAPTURE); echo "Splitting A Word into Letters"; print_r($array); ?> Explanation 1 This is the string we will be splitting on line 2. 2 The preg_split() function takes a number of arguments. In this example, the first argument is the delimiter. \s represents a whitespace character. The second argument is the string that is being split, $alpha. The third argument (normally omitted) is -1, stating that there is no limit to the number of array elements that can be created when splitting up this string. The PREG_SPLIT_OFFSET_CAPTURE flag says that for every array element created, the offset of where it occurred within the string will also be returned. You can see in the output of this example (Figure 12.13) that each substring is an array element, and its offset within the string is another array consisting of two elements, the array element (substring) and the offset position of where that substring was found in the original string. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Figure 12.13. Splitting up a string with the preg_split() function. Output from Example 12.12. Other related PHP functions are: spliti(), split(), implode(), and explode(). See Chapter 8, “Arrays,” for more on these. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
The preg_grep() Function Similar to the UNIX grep command, the preg_grep() function returns an array of values that match a pattern found in an array instead of a search string. You can also invert the search and get an array of all elements that do not contain the pattern being searched for (like UNIX grep -v) by using the PREG_GREP_INVERT flag. Format array preg_grep ( string pattern, array input [, int flags] ) Example: $new_array = preg_grep("/ma/", array("normal", "mama", "man","plan")); // $new_array contains: normal, mama, man $new_array=preg_grep("/ma/",array("normal","mama","man", "plan"),PREG_GREP_INVERT); // $new_array contains: plan Example 12.13. Code View: The preg_grep() Function The preg_grep() Function
3 After the array has been sorted, the preg_grep() function will search for the pattern, /Pat/, in each element of the array, and return and assign the matched array elements to another array called $newarray. 4 The count() function returns the number of elements in the new array; that is, the number of elements where the pattern /Pat/ was found. 5 The found elements are displayed. Note that the index values have been preserved. 6 When the PREG_GREP_INVERT flag is specified, the preg_grep() function will match and return any elements not found in the original array, as shown in the output in Figure 12.14. Figure 12.14. The preg_grep() function. Output from Example 12.13. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
12.2.3. Getting Control—The RegEx Metacharacters Regular expression metacharacters are characters that do not represent themselves. They are endowed with special powers to allow you to control the search pattern in some way (e.g., finding a pattern only at the beginning of the line, or at the end of the line, or if it starts with an upper- or lowercase letter). Metacharacters will lose their special meaning if preceded with a backslash. For example, the dot metacharacter represents any single character, but when preceded with a backslash is just a dot or period. If you see a backslash preceding a metacharacter, the backslash turns off the meaning of the metacharacter, but if you see a backslash preceding an alphanumeric character in a regular expression, then the backslash is used to create a metasymbol. A metasymbol provides a simpler form to represent some of regular expression metacharacters. For example, [0-9] represents numbers in the range between 0 and 9, and \d represents the same thing. [0-9] uses the bracketed character class, whereas \d is a metasymbol (see Table 12.6). Table 12.6. Metacharacters Character Class What It Matches Metacharacter Single characters and digits Matches any character except a newline. . [a-z0-9] (for more, see “Matching Matches any single character in a set. [^a-z0-9] Single Characters and Matches any single character not in a set. Digits” on page 524) Single characters and digits Matches one digit. \d \D —Metasymbols (for more, Matches a nondigit, same as [^0-9]. \w see “Metasymbols” on page Matches an alphanumeric (word) character. \W 530) Matches a nonalphanumeric (nonword) character. Whitespace characters Matches whitespace character, spaces, tabs, \s and newlines. Matches a nonwhitespace character. \S Matches a newline. \n Matches a return. \r Matches a tab. \t Matches a form feed. \f Matches a null character \0 Anchored characters (for Matches a word boundary. \b \B more see “Anchoring Matches a nonword boundary. ^ Metacharacters” on page Matches to beginning of line. Matches to end of line. $ 520) Matches the beginning of the string only. \A \D Matches the end of the string or line. Repeated characters (for Matches 0 or 1 occurrences of the letter x. x? more, see “Metacharacters to Repeat Pattern Matches” Matches 0 or more occurrences of the letter x* on page 533) x. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Table 12.6. Metacharacters Character Class What It Matches Metacharacter Matches 1 or more occurrences of the letter x+ x. Grouped characters (for Matches one or more patterns of xyz (e.g., (xyz)+ more, see “Grouping or xyxxyzxyz). Clustering.” on page 544) Matches at least m occurrences of the letter x, x{m,n} and no more than n occurrences of the letter x. Alternative characters (for Matches one of was, were, or will. was|were|will more, see “Metacharacters for Alternation” on page 543) Remembered characters Used for backreferencing. (string) \1 or $1 (for more, Matches first set of parentheses. Matches second set of parentheses. \2 or $2 see“Remembering or Matches third set of parentheses. \3 or $3 Capturing” on page 545) Positive lookahead and Matches x but does not remember the match. (?:x) lookbehind (for more, see These are called noncapturing parentheses. “Positive Lookahead” on page 550 and “Positive Matches x only if x is followed by y. For x(?=y) Lookbehind” on page 552 example, /Jack(?=Sprat)/ matches Jack only if it is followed by Sprat. /Jack(?=Sprat|Frost)/ matches Jack only if it is followed by Sprat or Frost. Neither Sprat nor Frost is kept as part of what was matched. Matches x only if x is not followed by y. For x(?!y) example, /\d+(?!\.)/ matches one or more numbers only if they are not followed by a decimal point. The following regular expression contains metacharacters: /^a...c/ The first metacharacter is a caret (^). The caret metacharacter matches for a string only if it is at the beginning of the line. The period (.) is used to match for any single character, including a space. This expression contains three periods, representing any three characters. To find a literal period or any other character that does not represent itself, the character must be preceded by a backslash to prevent interpretation. The expression reads: Search at the beginning of the line for a letter a, followed by any three single characters, followed by a letter c. It will match, for example, abbbc, a123c, a c, aAx3c, and so on, only if those patterns were found at the beginning of the line. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
In the following examples, we perform pattern matches, searches, and replacements based on the data from a text file called data.txt. In the PHP program, the file will be opened and, within a while loop, each line will be read. The functions discussed in the previous section will be used to find patterns within each line of the file. The regular expressions will contain metacharacters, described in Table 12.6. Anchoring Metacharacters Often it is necessary to find a pattern only if it is found at the beginning or end of a line, word, or string. The “anchoring” metacharacters (see Table 12.7) are based on a position just to the left or to the right of the character that is being matched. Anchors are technically called zero-width assertions because they correspond to positions, not actual characters in a string; for example, /^abc/ means find abc at the beginning of the line, where the ^ represents a position, not an actual character. Table 12.7. Anchors (Assertions) Metacharacter What It Matches ^ Matches to beginning of line or beginning of string. $ Matches to end of line or end of string. \A Matches the beginning of a string. \b Matches a word boundary. \B Matches a nonword boundary. \D Matches the end of a string. Beginning-of-Line Anchor The ^ metacharacter is called the beginning-of-line anchor. It is the first character in the regular expression and matches a pattern found at the beginning of a line or string. Example 12.14. Code View: (The file data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ------------------------------------------------------------------ (The PHP Program) Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
------------------------------------------------------------------ (Output) Betty Boop 200 BB Kingson 803 Explanation 1 The file data.txt is opened for reading. 2 As long as the end of file has not been reached, the while loop will continue to execute. 3 For each iteration of the loop, the fgets() function reads in a line of text. 4 The preg_match() function will return TRUE if a pattern consisting of a string beginning with a B is matched. 5 The lines that matched are printed. End-of-Line Anchor The end-of-line anchor, a dollar sign, is used to indicate the ending position in a line. The dollar sign must be the last character in the pattern, just before the closing forward slash delimiter of the regular expression, or it no longer means “end-of-line anchor.”[1] [1] If moving files between Windows and UNIX, the end-of-line anchor might not work. You can use programs such as dos2unix to address this problem. Example 12.15. Code View: (The File data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ---------------------------------------------------------------- (The PHP Program) ---------------------------------------------------------------- (Output) Steve Blenheim 100 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 Explanation 1 The file data.txt is opened for reading. 2 As long as the end of file hasn’t been reached, the while loop will continue to execute. 3 For each iteration of the loop, the fgets() function reads in a line of text. 4 The preg_match() function will return TRUE if a pattern consisting of a line ending with a 0 is matched. The $ metacharacter indicates that 0 must be followed by a newline. 5 The lines that matched are printed. Word Boundaries A word boundary is represented in a regular expression by the metasymbol \b. You can search for the word that begins with a pattern, ends with a pattern, or both begins and ends with a pattern; for example, /\blove/ matches a word beginning with the pattern love, and would match lover, loveable, or lovely, but would not find glove. /love\b/ matches a word ending with the pattern love, and would match glove, clove, or love, but not clover. /\blove\b matches a word beginning and ending with the pattern love, and would match only the word love. Example 12.16. Code View: (The File data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ---------------------------------------------------------------- (The PHP Script) Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
---------------------------------------------------------------- (The Output) Mama Bear 702 Explanation 1 The preg_match() function will return TRUE if a pattern consisting of the word bear is matched, and it is insensitive to case. Because the regular expression is anchored on both ends of the word with the word boundary metasymbol, \b, only bear is matched in $test, not “unbearable,” “beard,” or “bears.” 2 The lines that matched are printed. Matching Single Characters and Digits There are metacharacters to match single characters or digits, and single noncharacters or nondigits, whether in or not in a set. The Dot Metacharacter The dot metacharacter matches for any single character with exception to the newline character. For example, the regular expression /a.b/ is matched if the string contains a letter a, followed by any one single character (except the \n), followed by a letter b, whereas the expression /.../ matches any string containing at least three characters. To match on a literal period, the dot metacharacter must be preceded by a backslash; for example, /love\./ matches on love. not lover. Example 12.17. Code View: (The File data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ---------------------------------------------------------------- (The PHP Program) ---------------------------------------------------------------- (Output) Jon DeLoach 500 Explanation 1 The file data.txt is opened for reading. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
2 As long as the end of file has not been reached, the while loop will continue to execute. 3 For each iteration of the loop, the fgets() function reads in a line of text. 4 The regular expression /^... / contains the dot metacharacter. The regular expression means: go to the beginning (^) of the line and find any three characters, followed by a space. (The dot metacharacter does not match the newline character.) The only line that matched the pattern starts with Jon. It begins with three characters followed by a space. Example 12.18. Code View: (The File data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ---------------------------------------------------------------- (The PHP Program) ---------------------------------------------------------------- (Output) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Daniel DeLoach 500 Karen Evich 600 BB Kingson 803 Explanation 1 The text file data.txt is opened for reading. 2 Until the end of the file is reached, the while loop will continue looping, reading in one line at a time from the file. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
reading in one line at a time from the file. 3 The first argument to the preg_replace() function is a regular expression containing the dot metacharacter. If the regular expression (a capital J followed by at least two characters) is matched in $text, the found pattern will be replaced with Daniel. The Character Class A character class represents one character from a set of characters. For example, [abc] matches either an a, b, or c; [a-z] matches one character from a set of characters in the range from a to z; and [0-9] matches one character in the range of digits between 0 to 9. If the character class contains a leading caret ^, then the class represents any one character not in the set; for example, [^a-zA-Z] matches a single character not in the range from a to z or A to Z, and [^0-9] matches a single digit not in the range between 0 and 9 (see Table 12.8). Table 12.8. Character Classes Metacharacter What It Matches [abc] Matches an a or b or c. [a–z0–9_] Matches any single character in a set. [^a–z0–9_] Matches any single character not in a set. PHP provides additional metasymbols to represent a character class. The symbols \d and \D represent a single digit and a single nondigit, respectively (the same as [0-9] and [^0-9]); \w and \W represent a single word character and a single nonword character, respectively (the same as [A-Za-z_0-9] and [^A-Za-z_0-9]). If you are searching for a particular character within a regular expression, you can use the dot metacharacter to represent a single character, or a character class that matches on one character from a set of characters. In addition to the dot and character class, PHP supports some backslashed symbols (called metasymbols) to represent single characters. Matching One Character from a Set A regular expression character class represents one character out of a set of characters, as shown in Example 12.19. Example 12.19. Code View: (The File data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ---------------------------------------------------------------- (The PHP Program)
5 echo "$text"; } } ?> ---------------------------------------------------------------- (Output) Betty Boop 200 Igor Chevsky 300 Karen Evich 600 BB Kingson 803 Explanation 1 The file data.txt is opened for reading. 2 As long as the end of file has not been reached, the while loop will continue to execute. 3 For each iteration of the loop, the fgets() function reads in a line of text. 4 The regular expression /^[BKI]/ contains a character class matching a string that contains a single uppercase character from the set [BKI] meaning: a B or K or I. The preg_match() function will return TRUE if the pattern is matched. 5 These lines begin with one of the three characters B or K or I. Matching One Character in a Range A character class can also be represented as a range of characters by placing a dash between two characters, the first being the start of the range and the second the end of the range; for example, [0-9] represents one character in the range between 0 and 9 and [A-Za-z0-9] represents one alphanumeric character. If you want to represent a range between 10 and 13, the regular expression would be /1[0-3]/, not /[10-13]/ because only one character can be matched in a character class. Example 12.20. Code View: (The File data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ---------------------------------------------------------------- (The PHP Program)
5 echo "$text"; } } ?> ---------------------------------------------------------------- (Output) Mama Bear 702 Igor Chevsky 300 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 Explanation 1 The file data.txt is opened for reading. 2 As long as the end of file has not been reached, the while loop will continue to execute. 3 For each iteration of the loop, the fgets() function reads in a line of text. 4 The regular expression /[E-M]/ contains a character class matching a string that contains a single character from the range of characters between E and M. The preg_match() function will return TRUE if the pattern is matched. 5 Each of these lines contain an uppercase letter in the range between E and M. Example 12.21. Code View: (The File data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ---------------------------------------------------------------- (The PHP Program) Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
---------------------------------------------------------------- (Output) Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Explanation 1 The text file data.txt is opened for reading. 2 Until the end of the file is reached, the while loop will continue looping, reading in one line at a time from the file. 3 The first argument to the preg_match() function is a regular expression containing character classes using a range, [a-z] and [0-9]. The function will return TRUE if the pattern is matched in $text; that is, one lowercase letter in the range from a to z, a space, and a digit between 0 and 9. Matching One Character Not in a Set When a character set contains a caret right after the opening square bracket, then the search is inversed; that is, the regular expression represents one character not in the set or in the range. For example, [^a-z] represents one character that is not in the range between a and z. Example 12.22. Code View: (The File data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ---------------------------------------------------------------- (The PHP Program) ---------------------------------------------------------------- (Output) Mama Bear 702 Steve Blenheim 100 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Norma Cord 400 Jon DeLoach 500 Explanation 1 The text file data.txt is opened for reading. 2 Until the end of the file is reached, the while loop will continue looping, reading in one line at a time from the file. 3 The first argument to the preg_match() function is a regular expression containing character classes using a range, [^BKI]]. The function will return TRUE if the pattern is matched in $text; that is, the line begins with one character that is not a B or K or I. The ^ means “not” when enclosed in square brackets as part of a character set. Metasymbols Metasymbols offer an alternative way to represent a character class or whitespace characters (see Table 12.9). For example, instead of representing a number as [0-9], it can be represented as \d, and the alternative for representing a nonnumber [^0-9] is \D. Metasymbols are easier to use and and to type. Table 12.9. Metasymbols Character Symbol What It Matches Class \d One digit [0-9] \D One nondigit [^0-9] \w One word character [A-Za-z0-9_] \W One nonword character [^A-Za-z0-9] \s One whitespace character (tab, space, newline, carriage return, form feed, vertical tab) \S One nonspace character Metasymbols Representing Digits and Spaces The character class [0-9] represents one digit in the range between 0 and 9, as does the metasymbol \d. To create a regular expression that matches on three digits, you could write /[0-9][0-9][0-9]/ or simply /\d\d\d/. To represent a space, you can either insert a blank space, or use the metasymbol \s. Example 12.23. Code View: (The File data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ---------------------------------------------------------------- (The PHP Program) ---------------------------------------------------------------- (Output) Jon DeLoach 500 Karen Evich 600 Explanation 1 The text file data.txt is opened for reading. 2 Until the end of the file is reached, the while loop will continue looping, reading in one line at a time from the file. 3 The first argument to the preg_match() function is a regular expression containing the metasymbol \s representing a space, and \d representing a digit. The function will return TRUE if the pattern is matched in $text; that is, the line contains an h, followed by a space, and three digits. Metasymbols Representing Alphanumeric Word Characters The metasymbol to represent one alphanumeric word character is \w, much easier to write than [a-zA-Z0-9_]. To represent not one alphanumeric character, you simply capitalize the metasymbol, \W, which is the same as [^a-zA- Z0-9_]. Example 12.24. Code View: (The File data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ---------------------------------------------------------------- (The PHP Program)
2 while( ! feof($fh)){ $text = fgets($fh); 3 if(preg_match("/^\w\w\w\W/",$text)){ echo "$text"; } } ?> ---------------------------------------------------------------- (Output) Jon DeLoach 500 Explanation 1 The text file data.txt is opened for reading. 2 Until the end of the file is reached, the while loop will continue looping, reading in one line at a time from the file. 3 The first argument to the preg_match() function is a regular expression containing three alphanumeric word characters, \w\w\w. The \w represents the character class [A-Za-z0-9_]. The metasymbol \W represents the character class [^A-Za-z0-9_]. The function will return TRUE if the pattern is matched in $text; that is, the line begins with three alphanumeric word characters, followed by a character that is not an alphanumeric character. Example 12.25. Code View: (The File data.txt Contents) Mama Bear 702 Steve Blenheim 100 Betty Boop 200 Igor Chevsky 300 Norma Cord 400 Jon DeLoach 500 Karen Evich 600 BB Kingson 803 ------------------------------------------------------------------ (The PHP Program) ------------------------------------------------------------------ (Output) MamaXXear 702 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.