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Number   :  10658
Date     :  2005-02-28
Author   :  jeffneely2003
Subject  :  Re: Flatten Subdirectories?
Size(KB) :  6



--- In xxcopy@yahoogroups.com, "Garry Deane"  wrote:
> 
> --- In xxcopy@yahoogroups.com, "jeffneely2003"  
wrote:
> > Wow! Thanks a lot John. That was a very informative
> > introduction to Windows scripting for me. In fact, I had
> > to understand how it worked before I even tried running it
> > -- so I spent a few hours reading and testing some of those
> > commands that I'd never seen used before. I had no idea
> > batch scripting on Windows could do this.
> > 
> > Do you have any online scripting references you'd recommend?
> > 
> > I found these:
> > http://labmice.techtarget.com/articles/batchcmds.htm
> > http://www.ss64.com/nt/index.html
> > 
> > But I still never found anything that explained the usage of
> > ! as in:
> > set Y=!P:%SRC%=!
> > (assuming it is "evaluate", similar to using %)
> > 
> > Or what this does:
> > setlocal enabledelayedexpansion
> 
> To add to what John has already said, SETLOCAL localises
> environment variables so that they only exist within the
> section of batch code between a SETLOCAL...ENDLOCAL pair.
> After an ENDLOCAL keyword is reached, variables that have
> been newly defined after the SETLOCAL are discarded and
> previously defined variables are restored with their
> values from before the SETLOCAL. Try this bit of code to
> see localisation in action. Note that there is an implied
> endlocal when the end of the batch file is reached. If
> you use SETLOCAL within the batch file, all variables
> defined after that point will be discarded when the batch
> file terminates.
> 
> @echo off
> set var1=one
> setlocal
> set var1=one+one
> set var2=two
> echo [%var1%] [%var2%]
> endlocal
> echo [%var1%] [%var2%]
> 
> The ENABLEDELAYEDEXPANSION keyword allows variable expansion
> to be delayed until the variable is actually used. Delayed
> expansion variables are signified using surrounding ! instead
> of % e.g. !var1! rather than %var1%. Normally, when Cmd.exe
> reads a line of batch code and interprets what to do, the
> value of environment variables are substituted into the line
> very early in the parsing process. Any strings surrounded with
> % signs are replaced with the actual value of the matching
> environment variable name.
> 
> This process of variable substitution becomes important when
> using multiple commands on one line such as when using "&" or
> (...) to create compound command lines. If you have a multi
> command statement such as the following:
> 
> @echo off
> set var1=one
> (
> set var1=one+one
> set var2=two
> echo [%var1%] [%var2%]
> )
> echo [%var1%] [%var2%]
> 
> then everything between the parentheses are treated as one
> line. Cmd reads the entire (....) sequence up to the closing
> parenthesis then immediately substitutes the %var1% and %var2%
> pieces with the actual values of these variables. This happens
> BEFORE the "set var1=one+one" and "set var2=two" lines are
> executed so the values that are substituted are the values
> that existed before the first "(" is encountered i.e.
> var1=one and var2=nul.
> 
> This behaviour can be modified with the ENABLEDELAYEDEXPANSION
> keyword so that the substitution doesn't occur until the
> command containing the !var! is actually executed. Change
> the above code to the following and you'll see the difference.
> 
> @echo off
> set var1=one
> (
> set var1=one+one
> set var2=two
> echo [!var1!] [!var2!]
> )
> 
> This is the most command use of delayed expansion. In John's
> code however, he used a mix of ! and % to control the ORDER
> in which the variables were substituted. His line was similar
> to the following:
> 
> set P=abcd\defg
> set SRC=abcd
> set Y=!P:%SRC%=!
> 
> This gets substituted in the following way:
> 
> 1. Replace all %....% with the matching variable name
> set Y=!P:%SRC%=! -> set Y=!P:abcd=!
> 
> 2. Replace all !....! with the matching variable name
> set Y=!P:abcd=! -> set Y=!abcd\defg:abcd=! -> set Y=\defg
> 
> > A few follow-on questions came up while I was trying to
> > convert this into a full-fledged utility:
> > 
> > 1) How would I properly parameterize this so that the SRC
> > and DST could be passed in. And if the DST isn't passed, to
> > use a default dir that is the SRC + \output?
> 
> Batch parameters are accessed using %1, %2, %3 etc. to refer
> to the 1st through 3rd parameters (up to a max of 9). If you
> want to pass the src and dst as parameters, you would execute
> your batch command like this:
> 
> batch.bat "c:\Program Files\" d:\backup
> 
> Within the batch file you'd do something like this:
> 
> @echo off
> setlocal enabledelayedexpansion
> set src=%~1
> if not defined src set src=c:\Program Files\
> set dst=%~2
> if not defined dst set dst=d:\backup\
> 
> Another way to do the same thing might be:
> 
> @echo off
> setlocal enabledelayedexpansion
> set src=c:\Program Files\
> if not "%~1" == "" set src=%~1
> set dst=d:\backup\
> if not "%~2" == "" set dst=%~2
> 
> Note the use of the ~ in %~1. This strips out any quotes
> that may be used with paths that contain spaces and gives
> you the variable in a "known" unquoted state. You can then
> add your own qoutes as needed within subsequent commands.
> 
> > 2) How would I allow an optional parameter to be passed in
> > for the separator char, and use a default value if none is
> > passed?
> > 
> > eg FLATTEN SRC [DST] [/Sc]
> > where c is the separator char to use when flattening the dirs
> 
> This gets a bit trickier. Generally you'd do similar to
> the above for the paths and require that if a separator
> is used, it MUST be the 3rd parameter i.e. the [DST] parameter
> must be given even if it's the default value. If you want
> to allow both or all parameters to be optional, you need
> to examine the contents of the parameters to see whether
> any start with /S or /s. Possibly something like this
> (assumes that /S if given is the last parameter):
> 
> @echo off
> setlocal enabledelayedexpansion
> set src=c:\Program Files\
> set dst=d:\backup\
> set sep=
> 
> if "%~1" == "" goto :next
> set param=%~1
> if /i "%param:~0,2%" == "/s" (
> set sep=%~1&goto :next) else set src=%~1
> if "%~2" == "" goto :next
> set param=%~2
> if /i "%param:~0,2%" == "/s" (
> set sep=%~2&goto :next) else set dst=%~2
> if not "%~3" == "" set sep=%~3
> :next
> echo [%src%] [%dst%] [%sep%]
> 
> > 3) How would I create the DST dir if it doesn't exist?
> 
> As John has already explained, there's no need to do this
> as xxcopy will create it automatically if it doesn't exist.
> 
> Garry

Garry, thank you so much for further explaining the delayedexpansion 
setting. I tried some of the examples you posted to make sure I 
understood the way it works. It took a few runs for it to sink in, 
but I think I understand now.

Thanks again for the detailed explanation -- I really do appreciate 
the time you spent (and the time John spent) posting answers to my 
questions.

I've got a script now that does exactly what I wanted it to do.

-Jeff



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