having trouble with if exists command and variables

IMTheNachoMan · September 14, 2006, 3:49pm

I am trying to use the if exists command to check if a variable exists or not, but it is not working

try
	if some_var exists then DO SOMETHING
	if some_other_var exists then DO SOMETHING
on error e
	display dialog e
end try

if some_var exists then it actually gets to the some_other_var line
but if some_var does not exist, then it displays that dialog and stops

if i take them out of the try box
both lines run, but it displays an error box saying “blah blah variable does not exist”

how can i check if a variable exists or not?

thanks
-nacho

Matt-Boy · September 14, 2006, 4:01pm

Without the rest of your script, it’s hard to know if this will work for you, but I have done something similar in the past by defining a variable as a property with an initial empty value so I can check to see if it has been assigned a value later. I’m not aware if the “exists” command can be used in the way you are trying to use it.

property some_var : ""
property some_other_var : ""

if some_var is not "" then DO SOMETHING
if some_other_var is not "" then DO SOMETHING

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Bruce_Phillips · September 14, 2006, 4:02pm

AppleScript doesn’t have “unset” variables; Trying to get the value of a nonexistent error will throw the error you mentioned.

I think your on the right track. I think you just need to use separate try blocks.

try
	-- you could also say `get some_var` or even just `some_var`, but I think this makes the most sense when you read it
	some_var exists
	
	--DO SOMETHING
on error errMsg
	display dialog errMsg
end try

try
	some_other_var exists
	
	--DO SOMETHING
on error errMsg
	display dialog errMsg
end try

Would you tell us why you would have an undefined variable?

Edit:

FWIW, it does seem to work. (Though I doubt that it’s actual testing the existence of a variable; it’s probably just getting some kind of value and retuning true.)

set test to "abc"
test exists
--> true

I was going to suggest something like that. You may not want to use properties though, as that value will persist across multiple executions (until the script is recompiled). Unless you want persistence, you could just set some variables to an empty string.

set someVar to ""
set someOtherVar to ""
-- whatever else

IMTheNachoMan · September 14, 2006, 4:32pm

the reason i was doing it was
i have a varialbe thePerson which is an address book person
then i set variables (homephone, workphone) with values from thePerson

set homePhone to value of first phone whose label is "home"

but if person does not have a home phone # that var does not get set

then later i wanna populate a text field with that homePhone # if it exists

i sppose il have to use the set homephone to “” for now

thank you guys
-peace

Matt-Boy · September 14, 2006, 4:34pm

Good point about properties. I was referencing a print script I wrote, where the code that I copied was doing just what Bruce mentions - checks to see if the values you ran last time are still saved in the property. The first time you run the script, it has to check to see if there are saved values or not. Here is that part of my print script in case anyone might find some of it useful for setting up a script that saves the last settings as the “default” settings next time you run:

property RegMarks : ""
property IncludeTag : ""
property PDFResolution : ""

tell application "Finder"
		activate
		if RegMarks = "" or IncludeTag = "" or PDFResolution = "" then
			set RegMarks to the button returned of (display dialog "Registration marks?" buttons {"Yes", "No", "Cancel"} default button "Yes") as text
			set IncludeTag to the button returned of (display dialog "Include job slug/tag?" buttons {"Yes", "No", "Cancel"} default button "Yes") as text
			set PDFResolution to the button returned of (display dialog "High Res or Low Res PDF?" buttons {"High Res", "Low Res", "BOTH"} default button "Low Res")
		else
			try
				set ChangeInputQuery to the button returned of (display dialog ("Registration Marks: " & RegMarks & return & "Including job tag: " & IncludeTag & return & "PDF Resolution: " & PDFResolution & return & return & "Continue with these settings?") buttons {"OK", "Change", "Cancel"} default button "OK")
			on error
				return
			end try
			if ChangeInputQuery = "Change" then
				set RegMarks to the button returned of (display dialog "Registration marks?" buttons {"Yes", "No", "Cancel"} default button "Yes") as text
				set IncludeTag to the button returned of (display dialog "Include job slug/tag?" buttons {"Yes", "No", "Cancel"} default button "Yes") as text
				set PDFResolution to the button returned of (display dialog "High Res or Low Res PDF?" buttons {"High Res", "Low Res", "BOTH"} default button "Low Res")
			end if
		end if
end tell

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Operating System: Mac OS X (10.4)

mark_hunte · September 15, 2006, 2:25am

Here is an extract ( also slightly edited ) from one of my scripts to show you how to get any phone number that the person has.
The key is just to use the ‘label of phone’ and ‘value of phone’ of the person and the count them.
Hope it makes sense.

property the_numbers : {}
tell application "Address Book"
	
	set theentry to selection -- in this example just select one person (entry)
	set this_item2 to item 1 of theentry
	
	--Phone Numbers
	set the_phone_label to label of phone of this_item2 -- this gets ALL phone label names as a list
	
	set the_phone to value of phone of this_item2 -- this gets ALL phone values as a list
	set the_count to 0
	repeat with i from 1 to number of items in the_phone -- count the number of items in the list the_phone
		set the_count to the_count + 1 -- sets up a number counter
		set this_item to item i of the_phone -- gets the next tel number in list 
		set this_item to item the_count of the_phone_label & " Tel : " & this_item & return --this matches the list item of the_phone_label with its value from the list the_phone
		-- --set item the_count of the_phone to this_item as string
		copy this_item to end of the_numbers -- makes a new list with all the numbers and labels for that person matched
	end repeat
	
end tell

the_numbers

IMTheNachoMan · September 15, 2006, 5:12am

Bruce Phillips:

IMTheNachoMan:

how can i check if a variable exists or not?

AppleScript doesn’t have “unset” variables; Trying to get the value of a nonexistent error will throw the error you mentioned.

I think your on the right track. I think you just need to use separate try blocks.
try
	-- you could also say `get some_var` or even just `some_var`, but I think this makes the most sense when you read it
	some_var exists
	
	--DO SOMETHING
on error errMsg
	display dialog errMsg
end try

try
	some_other_var exists
	
	--DO SOMETHING
on error errMsg
	display dialog errMsg
end try
Would you tell us why you would have an undefined variable?

Edit:

Matt-boy:

I’m not aware if the “exists” command can be used in the way you are trying to use it.

FWIW, it does seem to work. (Though I doubt that it’s actual testing the existence of a variable; it’s probably just getting some kind of value and retuning true.)
set test to "abc"
test exists
--> true
Matt-Boy:

I have done something similar in the past by defining a variable as a property with an initial empty value

I was going to suggest something like that. You may not want to use properties though, as that value will persist across multiple executions (until the script is recompiled). Unless you want persistence, you could just set some variables to an empty string.
set someVar to ""
set someOtherVar to ""
-- whatever else

the problem with this is, say i have this

set x to ""
tell application "Address Book"
	-- set thePerson to some person in the address book
	set thePerson to some person
	tell thePerson
		display dialog x
	end tell
end tell

i get an error because it says that x is not defined
and that makes sense, x is not defined for thePerson
how can i access the ‘x’ that is outside of the tell blocks?

thanks
-nacho

mark_hunte · September 15, 2006, 9:41am

IMTheNachoMan:

the problem with this is, say i have this
set x to ""
tell application "Address Book"
	-- set thePerson to some person in the address book
	set thePerson to some person
	tell thePerson
		display dialog x
	end tell
end tell
i get an error because it says that x is not defined
and that makes sense, x is not defined for thePerson
how can i access the ‘x’ that is outside of the tell blocks?

thanks
-nacho

Actually, the extract you posted here on its own does in fact work, and does not give an error.
It may be worth posting more of you script to give a better idea of you your real end goal.

Again an example to get all the numbers the have. But this time put any that contain home, work, into the own variable list

set the_numbers to {}
set home_numbers to {}
set work_numbers to {}
set other_numbers to {}
tell application "Address Book"
	
	--set this_item2 to some person -- in this example just select one person (entry)
	set theentry to selection -- in this example just select one person (entry)
	
	set this_item2 to item 1 of theentry -- comment this line out if you use the 'some person' line above instead of the selection.
	
	--Phone Numbers
	set the_phone_label to label of phone of this_item2 -- this gets ALL phone label names as a list
	
	set the_phone to value of phone of this_item2 -- this gets ALL phone values as a list
	set the_count to 0
	repeat with i from 1 to number of items in the_phone -- count the number of items in the list the_phone
		set the_count to the_count + 1 -- sets up a number counter
		set this_item to item i of the_phone -- gets the next tel number in list 
		set this_item to item the_count of the_phone_label & " Tel : " & this_item & return --this matches the list item of the_phone_label with its value from the list the_phone
		
		copy this_item to end of the_numbers -- makes a new list with all the numbers and labels for that person matched
	end repeat
	
end tell

repeat with i from 1 to number of items in the_numbers
	set this_item to item i of the_numbers
	if this_item contains "home" then
		copy this_item to end of home_numbers
	else if this_item contains "work" then
		copy this_item to end of work_numbers
	else if this_item is not equal to "" then
		copy this_item to end of other_numbers
	end if
end repeat

home_numbers

Nigel_Garvey · September 15, 2006, 10:28am

Hi.

Going back to exists briefly, it’s an application-only command, according to the AppleScript Language Guide. That means you can test the existence of items belonging to applications that support it, but not to AppleScript language things like variables. The trick in this case would be to set the variable to one thing if the item exists and to something else if it doesn’t.

tell application "Address Book"
	set thePerson to some person
	tell (thePerson's first phone whose label is "home"
		if (it exists) then
			set homePhone to its value
		else
			set homePhone to missing value -- or "" or whatever.
		end if
	end tell
end tell

Another approach, shorter and possibly more useful, would be to set the variable to the value of every phone of the relevant label that the person might have. (This is similar to Mark’s idea.) The result in this case is a list containing either phone numbers or nothing.

tell application "Address Book"
	set thePerson to some person
	set homeNumbers to value of thePerson's phones whose label is "home"
	set workNumbers to value of thePerson's phones whose label is "work"
end tell

This way, the variable definitely exists and is definitely a list, which is easier to deal with than a variable that may or may not exist. And if the person has more than one number under that heading, you have them all together.