Common PHP Functions for Arrays, Strings, Dates, Files, and Directories

1. Common PHP Array Functions

(1) array() – create an array.

(2) in_array() – check if a value exists in an array.

(3) count() – return the number of elements in an array.

(4) array_merge() – merge multiple arrays into one.

(5) array_diff() – compute the difference between arrays.

(6) array_intersect() – get the intersection of arrays.

(7) array_keys() – retrieve all keys from an array.

(8) array_values() – retrieve all values from an array.

(9) array_unique() – remove duplicate values.

(10) array_push() – push one or more elements onto the end of an array.

(11) array_pop() – pop and return the last element of an array.

(12) array_walk() – apply a user‑defined callback to each element.

2. Common PHP String Functions

(1) trim() – strip whitespace (or other characters) from the beginning and end of a string.

(2) strlen() – get the length of a string.

(3) mb_strlen() – get the length of a multibyte string with a specified encoding.

(4) substr() – return a portion of a string.

(5) str_replace() – replace occurrences of a substring.

(6) str_repeat() – repeat a string a given number of times.

(7) is_string() – check whether a variable is a string.

(8) str_shuffle() – randomly shuffle characters in a string.

(9) sprintf() – return a formatted string.

(10) strstr() – find the first occurrence of a substring.

(11) addslashes() – escape characters with backslashes.

3. Common PHP Date/Time Functions

(1) date() – format a local date/time.

(2) getdate() – retrieve date/time information as an array.

(3) date_default_timezone_set() – set the default timezone.

(4) date_default_timezone_get() – get the default timezone.

(5) mktime() – get a Unix timestamp for a specific date.

(6) strtotime() – parse an English textual datetime description into a Unix timestamp.

(7) strftime() – format a local date/time according to locale settings.

4. Common PHP File Functions

(1) fopen() – open a file.

(2) fgets() – read a line from a file (note: file_get_contents() also reads files).

(3) fwrite() – write data to a file (note: file_put_contents() can also write files).

(4) fclose() – close an open file handle.

(5) rename() – move or rename a file.

(6) copy() – copy a file.

(7) vim or touch – create a new file.

(8) unlink() – delete a file.

(9) fileatime() – get the last access time of a file.

(10) filemtime() – get the last modification time of a file.

(11) filesize() – get the size of a file.

(12) filetype() – get the type of a file.

(13) stat() – retrieve detailed file status information.

(14) is_dir() – determine if a path is a directory.

5. Common PHP Directory Functions

(1) opendir() – open a directory.

(2) readdir() – read an entry from an open directory.

(3) rmdir() – remove a directory.

(4) closedir() – close a directory handle.

(5) mkdir() – create a new directory.

(6) dirname() – return the directory portion of a path.

(7) getcwd() – get the current working directory.

(8) scandir() – list files and directories inside a specified path.