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I have searched around quite a bit and have failed to find an answer. In AutoHotKey, I am not sure the difference when a single percent is used near the beginning of a line, and when a variable is enclosed between two percent signs. I usually use trial and error to find when I use one or the other, I am hoping someone could shed some light on what the difference is or explain what it is actually doing.

Here are some examples of this in action.

Example 1: I noticed if you have multiple variables along with text, scripts tend to go with the preceding percent. Such as:

some_val := Clipboard

loop 5
    msgbox % "Index:" . A_Index . ", variable:" . some_val

Example 2: I often see this as well, and sometimes it appears it must be used. Is this true?

some_variable := "test text to send"

Send, %some_variable%
wetin
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1 Answers1

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Wrapping in double percent signs is legacy AHK and basically there is no need to ever use it anymore. Only reason to wrap in double % would be being stuck behind in the old times, or maybe one could argue it also being more convenient, or something, to write in some cases, but I'm not buying it.
The legacy syntax is replaced by expression syntax.
The expression syntax is closer to how many other languages behave. AHK legacy syntax really is a mess.

All legacy commands (MsgBox for example) use the old legacy syntax on each parameter (unless otherwise specified).
If you specify a % followed up by a space at the start of the parameter, you're forcing AHK to evaluate an expression on that parameter instead of reading it as a legacy text parameter.
Example:
MsgBox, 5+5 We're using a legacy command, we're not starting the parameter off with a % and a space, so we're using the legacy syntax. The MsgBox is going to print the literal text 5+5 instead of 10.
MsgBox, % 5+5
Again, legacy command, but now we're forcing AHK to evaluate an expression here, 5+5.
The result of expression's evaluation is going to be passed onto the MsgBox command and the MsgBox is going to print 10.
If we wanted to MsgBox to print the literal text 5+5, and use the expression syntax to do it, we'd do MsgBox, % "5+5".
Quotation marks in expression syntax mean we're specifying a string.

Well then there's the problem of knowing when you're in expression syntax, and when you're in the legacy syntax.
By default, you're basically always in an expression.
You leave it by for example using a command or = to assign.
If the difference between a command and a function isn't clear to you, here's an example:
Command, % 7+3, % MyCoolArray[4], % SomeOtherNiceFunction(), % false
Function(7+3, MyCoolArray[4], SomeOtherNiceFunction(), false)
In the command we specified a % followed up by a space to evaluate the expressions on each parameter, and in the function, we didn't have to do that since we're already in an expression.

And if you're not clear on the difference between = and :=,
= is legacy and deprecated, it assigns plain text to a variable
:= assigns the result of an expression to a variable.

So that's what I could write from on top of my head.
If you had some more complex examples, I could try showing on them. Maybe convert some code you may have over to expression syntax, make it 100% free of legacy syntax.

And here's a good page on the documentation you should give a read:
https://www.autohotkey.com/docs/Language.htm

0x464e
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  • Thanks that clarifies the percent sign, but what's the comma doing after Command? – user3510079 Feb 02 '21 at 13:56
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    @user3510079 it just indicates that you're on the first parameter. The very first comma is optional/doesn't make a difference in most circumstances though, if that's what you meant by asking. – 0x464e Feb 02 '21 at 15:31