how to compare the first part of global replacing segment

ED Coder,

Your post is a bit confusing (to me, anyway), as I don't work much with HL7 on a daily basis, and I'm not sure what you mean by $GLOBAL, so I am going to try to clarify -- but I'll warn you, my crystal ball is usually pretty cloudy so I might be way off. If I am, I apologize in advance. But I hope this helps anyway.

Now, I'm going to assume that instead of $GLOBAL you really meant ^GLOBAL for where your info is stored -- as in, you've set up this info beforehand:

Set ^GLOBAL("123","bone issue")="Spur"   ; Sorry, but I added some data. You'll see why later.
Set ^GLOBAL("234","joint issue")="Ache"  ; Also on this one.

I'm going to assume one other thing for this post: that the local variable name that contains your data is called HLSEG. We can simulate this with this command:

Set HLSEG="$GLOBAL(""123"")"

Now, I realize that you may not be able to use carats (where I work we call 'em "uphats" -- don't ask me why...) in HL7 data so that's why you may have substituted the '$' symbol to indicate a global.

So, with those assumptions in place, here's a possible process on how you could get the data from a global into your segment.

First, if we assume that if the data doesn't start with a '$' symbol (indicating the need to reference a global) then just exit the process:

If $Extract(HLSEG,1)'="$" Quit

$Extract (in this case) gets just the first character of the HL Segment and if it isn't a '$' character then just quit. Here's documentation on $Extract: https://docs.intersystems.com/irislatest/csp/docbook/DocBook.UI.Page.cls?KEY=RCOS_FEXTRACT

If it does start with a '$' then we need to turn that into a carat. If your HL7 data can't contain '$' symbols beyond the first one, we can use the Translate function (documentation here: https://docs.intersystems.com/irislatest/csp/docbook/Doc.View.cls?KEY=RCOS_ftranslate )

 Set HLSEG=$Translate(HLSEG,"$","^")

That turns *all* '$' symbols to '^' in your variable, so if your HL7 data _could_ contain more '$' characters, this won't work for you. In that case, we'll just strip off the first character (no matter what it is), save the rest and prefix that with a '^':

 Set HLSEG="^"_$Extract(HLSEG,2,$Length(HLSEG))

Now that we have the actual global name in HLSEG, we can use the Indirection operator to access the global through HLSEG, and use the $Data function (documentation here: https://docs.intersystems.com/irislatest/csp/docbook/Doc.View.cls?KEY=RCOS_fdata )to see to see if that global exists:

 If $Data(@HLSEG)=0 Quit ; no data here.

$Data will return a '10' or '11' if there's a subnode (for ^GLOBAL("123") the subnode is "bone issue") so if there is, let's put that in the local variable SUBNODE - for that we need the $Order (documentation here: https://docs.intersystems.com/irislatest/csp/docbook/Doc.View.cls?KEY=RCOS_forder ) function:

 If $Data(@HLSEG)>9 Set SUBNODE=$Order(@HLSEG@(""))

Now SUBNODE will contain "bone issue". We can use the $Data function to see if that subnode actually contains data [[ this is why I changed your example a bit, to make it easier to demonstrate this ability ]], and if it does we'll put that in the ISSUE variable:

 If $Data(@HLSEG@(SUBNODE))#2=1 Set ISSUE=@HLSEG@(SUBNODE)

Now the variable ISSUE will contain "Spur".

Now that you have the info for the SUBNODE and ISSUE local variables populated, you should be able to  use them to assign what you need in your segments.

Again, it's possible I'm way off base on this and this didn't help you - if that's the case then I apologize but you might want to provide a more descriptive example of what you're trying to accomplish. I also apologize in retrospect if any of my code examples contain bugs. But I really do hope it helps you!