Hugh,
I had one last thought while reading this that might be a clever
approach. Read a little bit off the front of the currently running
stack (since you KNOW that's a valid stack) and compare it to the
file in question. The advantages are that you only have to read a
tiny bit of the file, and that the script should continue to work
even if/when Rev formats change. It's not foolproof - there's always
the chance that another type of file would have the same first bytes,
but it's probably very unlikely in practice and could always be
balanced with some sort of fatal error if the file did indeed end up
being bogus when you actually try to load it.
Reading from a file should be perfectly safe even if it is in use -
writing is the dangerous one. The only caveat I can think of is that
the current stack that you are using to compare against must exist on
disk and not *only* in memory.
function isAStack tFilePath
## the file path to the current stack
put value(word 2 of the long name of this stack) into tStackPath
## nibble off the first 8 bytes
open file tStackPath for binary read
read from file tStackPath for 8
put it into myFirst8Bytes
close file tStackPath
## check the first 8 bytes of the file in question
open file tFilePath for binary read
read from file tFilePath for 8
put it into testFirst8Bytes
close file tFilePath
## are they the same?
return (myFirst8Bytes = testFirst8Bytes)
end isAStack
Hi Klaus, Brian, David:
Good catches. I don't think I dare use open/read/close in case the
file (and
it could be any file) is in use, and testing the suffix is not always
reliable (I am allowing data stacks to be suffix-less). Since I've
never used a
shell script, I'm not sure what differentiates them from a
'normal' stack in
terms of initial stackfile characters. I don't think there are any
differences,
so a bit hard to be 100% foolproof it this case. Finally, since
this is for
ssBk and it is purposefully always saved in 2.4 format (as several
people have
requested for project compatibility purposes), I think I shall run
with my
original.
BUT your comments have been most instructive, and I thank you all.
/H
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