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": Use this function when the GPIB BUS gets stuck for some reason. You might be lucky and resolve the problem by calling this function |
| _viGTL | Go To Local mode: Instruments that accept this command will exit the "Remote Control mode" and go to "Local mode". If the instrument is already in "Local mode" this is simply ignored. Normally, if an instrument does not support this command it will simply stay in the "Remote Control mode" |
| _viOpen | Opens a VISA connection to an Instrument/Device |
| _viSetAttribute | Set any VISA attribute This function, which is called by _viSetTimeout, can ALSO be used to set the other VISA specific attributes. Read the VISA documentation for more information and a list of VISA attributes and their corresponding values. |
| _viSetTimeout | Sets the VISA timeout in MILISECONDS |