- String Manipulation:
strlen(): Returns the length of a string.strpos(), stripos(): Finds the position of the first occurrence of a substring in a string (case-sensitive or case-insensitive).substr(): Returns a part of a string.strtolower(), strtoupper(): Converts a string to lowercase or uppercase.str_replace(): Replaces all occurrences of a search string with a replacement string.
- Array Functions:
count(): Returns the number of elements in an array.array_push(), array_pop(): Adds/removes elements from the end of an array.array_shift(), array_unshift(): Adds/removes elements from the beginning of an array.array_merge(), array_combine(): Merges arrays or combines keys with values.array_key_exists(), in_array(): Checks if a key or value exists in an array.
- File Handling:
file_get_contents(), file_put_contents(): Reads from or writes to a file as a string.fopen(), fclose(): Opens and closes a file handle.fread(), fwrite(): Reads from or writes to an open file handle.fgets(), fgetcsv(): Reads a line or a CSV row from an open file handle.filesize(), file_exists(): Returns the size of a file or checks if a file exists.
- Date and Time Functions:
date(): Formats a timestamp into a human-readable date.time(): Returns the current Unix timestamp.strtotime(): Parses any English textual datetime description into a Unix timestamp.mktime(): Returns the Unix timestamp for a date.
- Math Functions:
abs(): Returns the absolute value of a number.round(), ceil(), floor(): Rounds a number to the nearest integer, upwards, or downwards.min(), max(): Returns the minimum or maximum value from a list of arguments.rand(), mt_rand(): Generates a random integer.
- Regular Expressions:
preg_match(), preg_replace(): Perform a regular expression match or replacement.preg_split(), preg_quote(): Splits a string by a regular expression or quotes regular expression characters.
- Miscellaneous:
isset(), empty(): Checks if a variable is set and not null or if it's empty.trim(), ltrim(), rtrim(): Removes whitespace or other characters from the beginning or end of a string.var_dump(), print_r(): Outputs information about a variable for debugging purposes.header(), redirect(): Sends a raw HTTP header or redirects the browser.