# EnvSub

Sets a variable to itself minus the given value (can also compare date-time values). Synonymous with: `Var -= Value`

.

EnvSub, Var, Value , TimeUnits
Var -= Value , TimeUnits
Var--

## Parameters

- Var
The name of the variable upon which to operate.

- Value
Any integer, floating point number, or expression (expressions are not supported when *TimeUnits* is present).

- TimeUnits
If present, this parameter directs the command to subtract *Value* from *Var* as though both of them are date-time stamps in the YYYYMMDDHH24MISS format. *TimeUnits* can be either Seconds, Minutes, Hours, or Days (or just the first letter of each of these). If *Value* is blank, the current time will be used in its place. Similarly, if *Var* is an empty variable, the current time will be used in its place.

The result is always rounded *down* to the nearest integer. For example, if the actual difference between two timestamps is 1.999 days, it will be reported as 1 day. If higher precision is needed, specify Seconds for *TimeUnits* and divide the result by 60.0, 3600.0, or 86400.0.

If either *Var* or *Value* is an invalid timestamp or contains a year prior to 1601, *Var* will be made blank to indicate the problem.

The built-in variable **A_Now** contains the current local time in YYYYMMDDHH24MISS format.

To precisely determine the elapsed time between two events, use the A_TickCount method because it provides millisecond precision.

To add or subtract a certain number of seconds, minutes, hours, or days from a timestamp, use EnvAdd (subtraction is achieved by adding a negative number).

## Remarks

This command is equivalent to the shorthand style: `Var -= Value`

.

Variables can be increased or decreased by 1 by using `Var++`

, `Var--`

, `++Var`

, or `--Var`

.

If either *Var* or *Value* is blank or does not start with a number, it is considered to be 0 for the purpose of the calculation (except when used *internally* in an expression and except when using the *TimeUnits* parameter).

If either *Var* or *Value* contains a decimal point, the end result will be a floating point number in the format set by SetFormat.

## Related

EnvAdd, EnvMult, EnvDiv, SetFormat, Expressions, If var is [not] type, SetEnv, FileGetTime

## Example

EnvSub, MyCount, 2
MyCount -= 2 *; Equivalent to above*
var1 = 20050126
var2 = 20040126
EnvSub, var1, %var2%, days
MsgBox, %var1% *; The answer will be 366 since 2004 is a leap year.*