Prepare your party hats: Batch File Week is almost over.
In your batch file,
you may want to exit batch file processing
(say, you encountered an error and want to give up),
but if you use the
that will exit the entire command processor.
Which is probably not what you intended.
Batch file processing ends when execution reaches
the end of the batch file.
The trick therefore is to use the
to jump to a label right before the end of the file,
so that execution “falls off the end”.
@echo off if "%1"=="" echo You must provide a file name.&goto end if NOT EXIST "\\server\backup\%USERNAME%\nul" mkdir "\\server\backup\%USERNAME%" if NOT EXIST "\\server\backup\%USERNAME%\nul" echo Unable to create output directory.&goto end copy "%1" "\\server\backup\%USERNAME%" :end
Here, there are two places where we abandon batch file execution. One is on an invalid parameter, and another is if the output directory couldn’t be created (or if it isn’t a directory at all).
The batch command interpreter provides a courtesy label
to simply this technique:
The special goto target
goto :eof (with the colon)
jumps to the end of the batch file.
It’s as if every batch file had a hidden goto label
:eof on the very last line.
goto :eof trick becomes even more handy
when you start playing with batch file subroutines.
Okay, let's back up: Batch file subroutines?
By using the
a batch file can invoke another batch file and regain
control after that other batch file returns.
(If you forget the
call, then control
does not return. In other words, the default mode
for batch file invocation is chain.)
In other words, the
lets you invoke another batch file as a subroutine.
The command line parameters are received by the
other batch file as the usual numbered parameters
It's annoying having to put every subroutine inside
its own batch file,
so the command interpreter folks added a way to
call a subroutine inside the same batch file.
The syntax for this is
call :label parameter parameter parameter.
This is logically equivalent to a batch file recursively
calling itself, except that execution begins at the
specified label instead of the first line of the file.
(It's as if a secret
goto label were added
to the top of the file.)
And since it is a batch file, execution of the called
subroutine ends when execution falls off the end of the file.
And that's where the special
comes in handy.
At the end of your subroutine,
you can jump to the end of the batch file (so that
execution falls off the end) by doing a
In other words,
goto :eof is the
for batch file subroutines.
Let's take it for a spin:
@echo off call :subroutine a b c call :subroutine d e f goto :eof :subroutine echo My parameters are 1=%1, 2=%2, 3=%3 goto :eof
goto :eof is redundant,
but it's probably a good habit to get into,
like putting a
break; at the end of
The subroutine technique is handy even if you don't
really care about the subroutine,
because stashing the arguments into the
parameters lets you use the
to process the inbound parameter.
@echo off call :printfilesize "C:\Program Files\Windows NT\Accessories\wordpad.exe" goto :eof :printfilesize echo The size of %1 is %~z1 goto :eof
Okay, this isn't actually much of a handy trick because you can also do it without a subroutine:
@echo off for %%i ^ in ("C:\Program Files\Windows NT\Accessories\wordpad.exe") ^ do echo The size of %%i is %%~zi
On the other hand, the subroutine trick combines well with the
since it lets you put complex content in the loop body
without having to mess with
@echo off setlocal set DISKSIZE=1474560 set CLUSTER=512 set DISKS=1 set TOTAL=0 for %%i in (*) do call :onefile "%%i" set /a DISKS=DISKS+1 echo Total disks required: %DISKS% endlocal goto :eof :onefile set /a SIZE=((%~z1 + CLUSTER - 1) / CLUSTER) * CLUSTER if %SIZE% GEQ %DISKSIZE% ( echo File %1 does not fit on a floppy - skipped goto :eof ) set /a TOTAL=TOTAL+SIZE if %TOTAL% GEQ %DISKSIZE% ( echo ---- need another disk set /a DISKS=DISKS+1 set /a TOTAL=SIZE ) echo copy %1 goto :eof
This program calculates the number of floppy disks it would take to copy the contents of the current directory without compression.
setlocal command takes a snapshot of the
environment for restoration when we perform the
at the end.
That will clean up our temporary variables when we're done.
The first two variables are parameters for the calculation, namely the disk capacity and the cluster size. (We're assuming that the root directory can hold all the files we may ultimately copy. Hey, this is just a demonstration, not a real program.)
The next two variables are our running total of the number of disks we've used so far, and how many bytes we've used on the last disk.
for command iterates over all the files in the
For each one, we call
:onefile with the file name.
:onefile subroutine does all the real work.
First, it takes the file size
%~z1 and rounds it up
to the nearest cluster.
It then sees if that size is larger than a floppy disk;
if so, then we're doomed, so we just skip the file.
Otherwise, we add the file to the current disk and see if it fits.
If not, then we declare the disk full and put the file on a brand
After the loop is complete, we print the number of floppy disks we calculated.
(This algorithm erroneously reports that no files require one disk. Fixing that is left as an exercise.)
There's your quick introduction to the secret
:eof label and batch file subroutines.
[Raymond is currently away; this message was pre-recorded.]