Sourcing vs executing

[user_deleted]

What is the difference between sourcing a script and executing it? By reading the online docs, they sound about the same, so I guess there must be a subtle difference.

[gmask]

I think sourcing reads the script from the file browser and "loads" it whereas execute loads whatever is allready typed into the script editor.

[macaronikazoo]

it depends on how the script is written. If the script is literally just code in a .mel file, without procedures etc, sourcing is exactly the same as executing.

however, if your script is just a collection of procedures, sourcing forces maya to re-loads those procedures from the script file. See, when u run a script for the first time, maya loads all the procedure code into memory, and doesn't bother reading them from disk again. So sourcing forces it to re-load from disk.

its a pretty big difference, but only if you write scripts in the form of procedures. Some people tend to just write in their script files without organising it into procedures (which is fine, but not terribly useful should u want to reuse that code...)

[naughty]

sourcing and executing are two totally different things.

You can only Source a file and you can only Execute a procedure(command).

when you use the source command you specify a file. Maya reads in all the code in the file and as long as there are only procedures in it will not actually execute anything. Sourcing will only execute something if there is an explicit MEL command in the file (outside a procedure definition)

When you execute a command however, Maya simply runs that command from it's knowledge of what is currently in memory. If it doesn't have the given command in memory it will search all your user scripts folders for a MEL file with that name. If it finds one it will SOURCE it and then, if it finds a proc within that file with the same name it will execute that procedure.
That's why it appears you can execute a file when in fact that isn't what you are doing.

That is why, once you've "executed" a script, any changes you make to it have no effect in maya until you source it because maya already has the command in memory.

Hope that clears up the difference.

:nathaN

[campbell]

interestingly, ive noticed that sourceing a file by explicit sourcing is different from sourcing a file by 'auto-sourcing' (the filename match) :

if this is saved into a file delThis.mel:

print "out proc";
global proc delThis(){
print "in proc";
}

delThis, will print 'in proc',
source delThis, will print 'out proc',

... auto-sourcing appears not to execute commands outside procs, whereas explicit sourcing does. but other proc-external stuff may still be parsed, eg:

print "out proc";
global proc delThis(){
print "in proc";
}
global int $gInter = 42;
circle;

will produce a circle for source delThis, but not for just delThis (which, obviously, has to always be run before an explicit source, so it does actually do an auto-source).
however, both forms of sourcing will declare and initialise the global int.

just something to keep in mind.

need to check on how boot-up sourcing behaves too.