array()

The array() function allows you to manually assign values to an array. Here is the syntax of the array() function:

$array_name = array("val1", "val2", "val3", ...);

array_push()

The array_push() function allows you to add one or more elements to the end of an existing array. Its syntax is

array_push($array_name, "element 1", "element 2", ...);

array_pop()

The array_pop() function allows you to take (pop) off the last element of an existing array. Its syntax is

array_pop($array_name);

array_unshift()

The array_unshift() function allows you to add elements to the beginning of an existing array. Its syntax is

array_unshift($array_name, "element 1", "element 2", ...);

array_shift()

The array_shift() function allows you to take (pop) off the first element of an existing array. Its syntax is

array_shift($array_name);

array_merge()

The array_merge() function allows you to combine two or more existing arrays. Its syntax is

array_merge($array1, $array2, ...);

array_keys()

The array_keys() function returns an array of all the key names in an existing array. Its syntax is

array_keys($array_name);

array_values()

The array_values() function returns an array of all the values in an existing array. Its syntax is

array_values($array_name);

count()

The count() function counts the number of elements in a variable. It's normally used to count the number of elements in an array, because any variable that is not an array has only one element—itself.

In the following example, $a is assigned a value equal to the number of elements in the $colors array:

$a = count($colors);

If $colors contains the values blue, black, red, and green, $a will be assigned a value of 4.

each() and list()

The each() and list() functions usually appear together, in the context of stepping through an array and returning its keys and values. Here is the syntax for these functions:

each(arrayname);
list(val1, val2, val3, ...);

For example, when you submit an HTML form via the GET method, each key/value pair is placed in the global variable $_GET. If your form input fields are named first_name and last_name and the user enters values of Joe and Smith, the key/value pairs are first_name/Joe and last_name/Smith. In the $_GET array, these variables are represented as the following:

$_GET["first_name"] // value is "Joe"
$_GET["last_name"] // value is "Smith"

You can use the each() and list() functions to step through the array in this fashion, printing the key and value for each element in the array:

while (list($key, $val) = each($_GET)) {
 echo "$key has a value of $val<br>";
}

reset()

The reset() function rewinds the pointer to the beginning of the array. Its syntax is

reset($array_name);

shuffle()

The shuffle() function randomizes the elements of a given array. Its syntax is

shuffle($array_name);

sizeof()

The sizeof() function counts the number of elements in an array. In the following example, $a is assigned a value equal to the number of elements in the $colors array:

$a = sizeof($colors);

If $colors contains the values blue, black, red, and green, $a is assigned a value of 4.

mysql_connect()

This function opens a connection to MySQL. It requires a server name, username, and password:

$connection = mysql_connect("servername","username","password");

mysql_select_db()

This function selects a database on the MySQL server for use by subsequent queries. It requires a valid established connection:

$db = mysql_select_db("myDB", $connection);

mysql_query()

This function issues the SQL statement. It requires an open connection to the database:

$sql_result = mysql_query("SELECT * FROM SOMETABLE",$connection);

mysql_error()

This function returns a meaningful error message when something goes wrong with your connection or query. It's normally used in the context of the die() function, like this:

$sql_result = mysql_query("SELECT * FROM SOMETABLE",$connection)
     or die(mysql_error());

mysql_fetch_array()

This function automatically places the SQL statement result row into an array:

$row = mysql_fetch_array($sql_result);

mysql_num_rows()

This function returns the number of rows in a result set:

$num = mysql_num_rows($sql_result);

date()

The date() function returns the current server timestamp, formatted according to a given set of parameters. Its syntax is

date(format, [timestamp]);

If the timestamp parameter is not provided, the current timestamp is assumed. Table B.7 shows the available formats.

checkdate()

The checkdate() function validates a given date. Successful validation means that the year is between 0 and 32767, the month is between 1 and 12, and the proper number of days is in each month (leap years are accounted for). Its syntax is

checkdate(month, day, year);

mktime()

The mktime() function returns the Unix timestamp as a long integer (in the format of seconds since the Epoch, or January 1, 1970) for a given date. Thus, the primary use of mktime() is to format dates in preparation for mathematical functions and date validation. Its syntax is

mktime(hour, minute, second, month, day, year);

time() and microtime()

The time() function returns the current system time, measured in seconds since the Epoch. The syntax of time() is simply

time();

You could get a result such as 958950466.

Using microtime() adds a count of microseconds, so instead of just receiving a result like 958950466, you would get a result like 0.93121600 958950466, at the exact moment you asked for the time since the Epoch (this includes both seconds and microseconds).

chmod(), chgrp(), and chown()

Like the shell commands of the same name, the chmod(), chgrp(), and chown() functions modify the permissions, group, and owner of a directory or file. Here is the syntax of these functions:

chmod("filename", mode);
chmgrp("filename", newgroup);
chown("filename", newowner);

In order to change permissions, groups, and owners, the PHP user must be the owner of the file, or the permissions must already be set to allow such changes by that user.

copy()

The copy() function works much like the cp shell command: It needs a filename and a destination in order to copy a file. The syntax of copy() is

copy("source filename", "destination");

The PHP user must have permission to write into the destination directory, or the copy() function will fail.

fopen()

The fopen() function opens a specified file or URL for reading and/or writing. The syntax of fopen() is

fopen("filename", "mode")

To open a URL, use http:// or ftp:// at the beginning of the filename string. You can open URLs only for reading, not writing.

If the filename begins with anything else, the file is opened from the file system and a file pointer to the opened file is returned. Otherwise, the file is assumed to reside on the local file system.

The specified mode determines whether the file is opened for reading, writing, or both. Table B.8 lists the valid modes.

fread()

Use the fread() function to read a specified number of bytes from an open file pointer. Its syntax is

fread(filepointer, length);

fputs()

The fputs() function writes to an open file pointer. Its syntax is

fputs(filepointer, content, [length]);

The file pointer must be open in order to write to the file. The length parameter is optional. If it isn't specified, all specified content is written to the file.

fclose()

Use the fclose() function to close an open file pointer. Its syntax is

fclose(filepointer);

mkdir()

Like the mkdir shell command, the mkdir() function creates a new directory on the file system. Its syntax is

mkdir("pathname", mode);

The PHP user must have write permission in the specified directory.

rename()

As its name suggests, the rename() function attempts to give a new name to an existing file. Its syntax is

rename("oldname", "newname");

The PHP user must have permission to modify the file.

rmdir()

Like the rmdir shell command, the rmdir() function removes a directory from the file system. Its syntax is

rmdir("pathname");

The PHP user must have write permission in the specified directory.

symlink()

The symlink() function creates a symbolic link from an existing file or directory on the file system to a specified link name. Its syntax is

symlink("targetname", "linkname");

The PHP user must have write permission in the specified directory.

unlink()

The unlink() function deletes a file from the file system. Its syntax is

unlink("filename");

The PHP user must have write permission for this file.

header()

The header() function outputs an HTTP header string, such as a location redirection. This output must occur before any other data is sent to the browser, including HTML tags.

For example, to use the header() function to redirect a user to a new location, use this code:

header("Location: http://www.newlocation.com");
exit;

setcookie()

The setcookie() function sends a cookie to the user. Cookies must be sent before any other header information is sent to the web browser. The syntax for setcookie() is

setcookie("name", "value", "expire", "path", "domain", "secure");

For example, you would use the following code to send a cookie called username with a value of joe that is valid for one hour within all directories on the testcompany.com domain:

setcookie("username","joe", time()+3600, "/", ".testcompany.com");

ceil()

The ceil() function rounds a fraction up to the next higher integer. Its syntax is

ceil(number);

decbin() and bindec()

The decbin() and bindec() functions convert decimal numbers to binary numbers and binary numbers to decimal numbers, respectively. The syntax of these functions is

decbin(number);
bindec(number);

dechex() and hexdec()

The dechex() and hexdec() functions convert decimal numbers to hexadecimal numbers and hexadecimal numbers to decimal numbers, respectively. The syntax of these functions is

dechex(number);
hexdec(number);

decoct() and octdec()

The decoct() and octdec() functions convert decimal numbers to octal numbers and octal numbers to decimal numbers, respectively. The syntax of these functions is

decoct(number);
octdec(number);

floor()

The floor() function rounds a fraction down to the next lower integer. Its syntax is

floor(number);

number_format()

The number_format() function returns the formatted version of a specified number. Its syntax is

number_format("number", "decimals", "dec_point", "thousands_sep");

For example, to return a formatted version of the number 12156688 with two decimal places and a comma separating each group of thousands, use

echo number_format("12156688","2",".",",");

The result is 12,156,688.00.

If only a number is provided, the default formatting does not use a decimal point and puts a comma between every group of thousands.

pow()

The pow() function returns the value of a given number raised to the power of a given exponent. Its syntax is

pow(number, exponent);

rand()

The rand() function generates a random value from a specific range of numbers. Its syntax is

rand(min, max);

round()

The round() function rounds a fraction to the next higher or next lower integer. Its syntax is

round(number);

sqrt()

The sqrt() function returns the square root of a given number. Its syntax is

sqrt(number);

srand()

The srand() function provides the random number generator with a set of possible values. Its syntax is

srand(seed);

A common practice is to seed the random number generator by using a number of microseconds:

srand((double)microtime()*1000000);

die()

The die() function outputs a given message and terminates the script when a returned value is false. Its syntax is

die("message");

For example, you would use the following code to print a message and stop the execution of your script upon failure to connect to your database:

$connection = mysql_connect("servername", "username", "password")
     or die ("Can't connect to database.");

exit

The exit statement terminates the execution of the current script at the point where the exit statement is made.

sleep() and usleep()

The sleep() and usleep() functions put a pause, or a delay, at a given point in the execution of your PHP code. The syntax of these functions is

sleep(seconds);
usleep(microseconds);

The only difference between sleep() and usleep() is that the given wait period for sleep() is in seconds, and the wait period for usleep() is in microseconds.

uniqid()

The uniqid() function generates a unique identifier with a prefix if you want one. Its syntax is

uniqid("prefix");

That's boring, though. Suppose you want a unique ID with a prefix of phpuser. You would use

$id = uniqid("phpuser");
echo "$id";

and you would get something like phpuser38b320a6b5482.

But if you use something really cool like

$id = md5(uniqid(rand()));
echo "$id";

you would get an ID like 999d8971461bedfc7caadcab33e65866.

exec()

The exec() function executes an external program. Its syntax is

exec(command, [array], [return_var]);

If an array is specified, the output of the exec() function will append to the array. If return_var is specified, it will be assigned a value of the program's return status.

For example, you would use the following code to perform a ping of a server five times and print the output:

$command = "ping -c5 www.thickbook.com";
exec($command, $result, $rval);
for ($i = 0; $i < sizeof($result); $i++) {
     echo "$result[$i]<br>";
}

passthru()

Like the exec() function, the passthru() function executes an external program. The difference between the two is that passthru() returns the raw output of the action. The syntax of passthru() is

passthru(command, return_var);

If return_var is specified, it will be assigned a value of the program's return status.

system()

The system() function executes an external program and displays output as the command is being executed. Its syntax is

system(command, [return_var]);

If return_var is specified, it will be assigned a value of the program's return status.

For example, you would use the following code to perform a ping of a server five times and print the raw output:

$command = "ping -c5 www.thickbook.com";
system($command);

ereg_replace() and eregi_replace()

The ereg_replace() and eregi_replace() functions replace instances of a pattern within a string and return the new string. The ereg_replace() function performs a case-sensitive match, and eregi_replace() performs a case-insensitive match. Here is the syntax for both functions:

ereg_replace(pattern, replacement, string);
eregi_replace(pattern, replacement, string);

For example, you would use the following code to replace "ASP" with "PHP" in the string "I really love programming in ASP!"

$old_string = "I really love programming in ASP!";
$new_string = ereg_replace("ASP", "PHP", $old_string);
echo "$new_string";

If "ASP" is mixed case, such as "aSp", use the eregi_replace() function:

$old_string = "I really love programming in aSp!";
$new_string = eregi_replace("ASP", "PHP", $old_string);
echo "$new_string";

split()

The split() function splits a string into an array using a certain separator (comma, colon, semicolon, and so on). Its syntax is

split(pattern, string, [limit]);

The limit is optional. If a limit is specified, the split() function stops at the named position—for example, at the tenth value in a comma-delimited list.

Session-Handling Functions

Session handling is a way of holding on to data as a user navigates your website. Data can be variables or entire objects. These simple functions are just a few of the session-related functions in PHP; see the PHP manual at http://www.php.net/ manual/ for more.

session_start()

The session_start() function starts a session if one has not already been started, or it resumes a session if the session ID is present for the user. This function takes no arguments and is called simply by placing the following at the beginning of your code:

session_start();

session_destroy()

The session_destroy() function effectively destroys all the variables and values registered for the current session. This function takes no arguments and is called simply by placing the following in your code:

session_destroy();

addslashes() and stripslashes()

The addslashes() and stripslashes() functions are very important when inserting and retrieving data from a database. Often, text inserted into a database will contain special characters (single quotes, double quotes, backslashes, NULL) that must be escaped before being inserted. The addslashes() function does just that, using this syntax:

addslashes(string);

Similarly, the stripslashes() function returns a string with the slashes taken away, using this syntax:

stripslashes(string);

chop(), ltrim(), and trim()

All three of these functions remove errant white space from a string. The chop() function removes white space from the end of a string, and ltrim() removes white space from the beginning of a string. The trim() function removes both leading and trailing white space from a string. Here is the syntax of these functions:

chop(string);
ltrim(string);
trim(string);

echo()

The echo() function returns output. The syntax of echo() is

echo (parameter 1, parameter 2, ...)

For example:

echo "I'm using PHP!";      // output is: I'm using PHP!
echo 2+6;                  // output is: 8

The parentheses are not required when using echo.

explode() and implode()

The explode() function splits a string using a given separator and returns the values in an array. The syntax of explode() is

explode("separator", "string");

For example, the following code takes a string called $color_list, containing a comma-separated list of colors, and places each color into an array called $my_colors:

$color_list = "blue,black,red,green,yellow,orange";
$mycolors = explode(",", $color_list);

Conversely, the implode() function takes an array and makes it into a string, using a given separator. The syntax of implode() is

implode("separator", "string");

For example, the following code takes an array called $color_list and then creates a string called $mycolors, containing the values of the $color_list array, separated by commas:

$mycolors = implode(",", $color_list);

htmlspecialchars() and htmlentities()

The htmlspecialchars() and htmlentities() functions convert special characters and HTML entities within strings into their acceptable entity representations. The htmlspecialchars() function converts only the less-than sign (< becomes &lt;), greater-than sign (> becomes &gt;), double quotes ("" becomes &quot;), and the ampersand (& becomes &amp;).

The htmlentities() function converts the characters in the ISO-8859-1 character set to the proper HTML entity. Here is the syntax of these functions:

htmlspecialchars(string);
htmlentities(string);

nl2br()

The nl2br() function replaces all ASCII newlines with the HTML line break (<BR>). The syntax of the nl2br() function is

nl2br(string);

sprintf()

The sprintf() function returns a string that has been formatted according to a set of directives, as listed in Table B.9. The syntax of sprintf() is

sprintf(directives, string);

For example, to turn the number 5 into $5.00 (five dollars), use:

$newnumber = sprintf("%0.02f", 5);

strlen()

The strlen() function returns the length of a given string. Its syntax is

strlen(string);

strtolower()

The strtolower() function returns a given string with all alphabetic characters in lowercase. Its syntax is

strtolower(str);

strtoupper()

The strtoupper() function returns a given string with all alphabetic characters in uppercase. Its syntax is

strtoupper (str);

substr()

The substr() function returns a portion of a string, given a starting position and optional ultimate length. Its syntax is

substr(string, start, [length]);

If the start position is a positive number, the starting position is counted from the beginning of the string. If the start position is negative, the starting position is counted from the end of the string.

Similarly, if the optional length parameter is used and is a positive number, the length is counted from the beginning of the string. If the length parameter is used and is a negative number, the length is counted from the end of the string.

For example:

$new_string = substr("PHP is great!", 1);      // returns "HP is great!"
$new_string = substr("PHP is great!", 0, 7);   // returns "PHP is "
$new_string = substr("PHP is great!", -1);     // returns "!"
$new_string = substr("PHP is great!", -6, 5);  // returns "great"

ucfirst()

The ucfirst() function changes the first alphabetic character in a string to an uppercase character. Its syntax is

ucfirst(string);

ucwords()

The ucwords() function changes the first letter of each word in a string to uppercase. Its syntax is

ucwords(string);