Below is a complete list of the user defined functions available in AutoIt. Click on a user defined function name for a detailed description.
| User Defined Function | Description |
| _ArrayAdd | Adds a specified value at the end of an array, returning the adjusted array. |
| _ArrayBinarySearch | Uses the binary search algorithm to search through a 1-dimensional array. |
| _ArrayCreate | Create a small array and quickly assign values. |
| _ArrayDelete | Deletes the specified element from the given array, returning the adjusted array. |
| _ArrayDisplay | Displays a 1-dimensional array in a message box. |
| _ArrayInsert | Inserts the a new string at the specified element into an array, returning the adjusted array. |
| _ArrayMax | Returns the highest value held in an array. |
| _ArrayMaxIndex | Returns the index where the highest value occurs in the array. |
| _ArrayMin | Returns the lowest value held in an array. |
| _ArrayMinIndex | Returns the index where the lowest value occurs in the array. |
| _ArrayPop | Returns the last element of an array, deleting that element from the array at the same time. |
| _ArrayReverse | Takes the given array and reverses the order in which the elements appear in the array. |
| _ArraySort | Sort a mutiple dimensional Array. |
| _ArraySwap | Swaps two elements of an array. |
| _ArrayToClip | Sends the contents of an array to the clipboard. |
| _ArrayToString | Places the elements of an array into a single string, separated by the specified delimiter. |
| _ArrayTrim | Trims all elements in an array a certain number of characters. |
| _Ceil | Returns the smallest integer greater than or equal to the specified value. |
| _ColorGetBlue | Returns the blue component of a given color. |
| _ColorGetGreen | Returns the green component of a given color. |
| _ColorGetRed | Returns the red component of a given color. |
| _DateAdd | Calculates a new date based on a given date and add an interval. |
| _DateDayOfWeek | Returns the name of the weekday, based on the specified day. |
| _DateDaysInMonth | Returns the number of days in a month, based on the specified month and year. |
| _DateDiff | Returns the difference between 2 dates, expressed in the type requested. |
| _DateIsLeapYear | Checks a given year to see if it is a leap year. |
| _DateIsValid | Checks the given date to determine if it is a valid date. |
| _DateTimeFormat | Returns the date in the PC's regional settings format. |
| _DateToDayValue | Split a string containing Date and Time into two separate Arrays. |
| _DateToDayOfWeek | Returns the weekdaynumber for a given date. |
| _DateToDayValue | Returns the daynumber since since noon 4713 BC January 1 for a given Gregorian date. |
| _DayValueToDate | Add the given days since noon 4713 BC January 1 and returns the Gregorian date. |
| _FileCountLines | Returns the number of lines in the specified file. |
| _FileCreate | Creates or zero's out the length of the file specified. |
| _FileReadToArray | Reads the specified file into an array. |
| _FileWriteLog | Writes current date,time and the specified text to a log file. |
| _Floor | Returns the greatest integer less than or equal to the specified value. |
| _GetIP | Get public IP address of a network/computer. |
| _HexToString | Convert a hex string to a string. |
| _Iif | Perform a boolean test within an expression. |
| _INetExplorerCapable | Converts a string to IE(Internet Explorer) capable line |
| _INetMail | Opens default user's mail client with given address, subject, and body. |
| _MathCheckDiv | Checks if NumA is divisable by NumB |
| _Max | Evaluates which of the two numbers is higher. |
| _Min | Evaluates which of the two numbers is lower. |
| _Now | Returns the current Date and Time in PC's format. |
| _NowCalc | Returns the current Date and Time in format YYYY/MM/DD HH:MM:SS for use in date calculations. |
| _NowCalcDate | Returns the current Date in format YYYY/MM/DD. |
| _NowDate | Returns the current Date in the Pc's format. |
| _NowTime | Returns the current Time in format HH:MM:SS. |
| _RunDos | Executes a DOS command in a hidden command window. |
| _StringEncrypt | An RC4 based string encryption function. |
| _StringProper | Changes a string to proper case, same a =Proper function in Excel |
| _StringRepeat | Repeats a string a specified number of times. |
| _StringReverse | Reverses the contents of the specified string. |
| _StringToHex | Convert a string to a hex string. |
| _TempFile | Generate a name for a temporary file. The file is guaranteed not to already exist in the user's %TEMP% directory. |
| _TicksToTime | Converts the specified tick amount to hours, minutes, and seconds. |
| _TimeToTicks | Converts the specified hours, minutes, and seconds to ticks. |
| _viOpen | Closes a VISA connection to an Instrument/Device |
| _viExecCommand | Send a Command/Query to an Instrument/Device through the VISA interface (GPIB / TCP) |
| _viFindGpib | Send a Command/Query to an Instrument/Device through the VISA interface (GPIB / TCP) |
| _viGpibBusReset | GPIB BUS "reset": |
| _viGTL | Go To Local mode: |
| _viOpen | Opens a VISA connection to an Instrument/Device |
| _viSetAttribute | Set any VISA attribute |
| _viSetTimeout | Sets the VISA timeout in MILISECONDS |