Windows Server 2008 : Creating Batch Files (part 2)

4. Clearing the Screen with cls

The cls command is useful within a batch file to clear the screen. It is entered simply as cls without any parameters. When entered, it clears the screen and puts the cursor at the top of the screen.

5. Calling Another Batch File with call

You can launch a batch file from within another batch file with the call command. The basic syntax is

call batchFileName

Figure 1 shows the order of processing when calling a batch file. Calltest.bat runs until it comes to the call calledbatch.bat line. It stops running and control is then passed to the called batch file, calledbatch.bat. After the called batch file runs, control passes back to the calling batch file.

Figure 1. Order of processing when calling a batch file

Figure 2 shows the output when the batch file is run from the command prompt and calls the second batch file.

Figure 2. Output of batch file calling another batch file

Note

If the called batch file doesn’t exist or somehow fails, control is still returned to the calling batch file. The call command works only from within a batch file. If you execute it directly from the command prompt, it is ignored.

The following table shows some use of the call command within a batch file.

Using the call Command	Comments
call newbatch.bat	Calls the newbatch.bat batch file. The file must exist in the current path or in a path known by the system.
call c:\scripts\newbatch.bat	Calls the newbatch.bat batch file located in the c:\scripts folder. If the batch file doesn’t exist, the call fails and control returns to the calling batch file.
call newbatch.bat batch parameters	If the called batch program accepts parameters, you can include them in the call.
call newbatch.bat :Label	Calls the batch program and starts execution at the specified label.

6. Changing the Order of Processing with goto

You can use the goto statement to change the order of processing of a batch file. Normally, a batch file goes through the lines in the batch file from the first line to the last line. However, there are times you want to skip some areas of the batch file. The basic syntax of the goto statement in the batch file is

goto label

The label is listed elsewhere in the document as a string of characters beginning with a colon (:). For example, you can have a label at the end of the batch file named :eof. You can then include the following lines in the batch file:

Using the goto Command	Comments
goto eof	The next command is at the :eof label. Notice that the label includes the colon (:), as in :eof, but the goto statement does not include the colon.
repadmin /syncall	This command never executes in this batch file because the goto eof statement always causes it to be skipped.
:eof	This is the eof label.
echo Exiting batch file	The echo command gives the user feedback.

7. Checking Conditions with if

When creating a batch file, you might occasionally want to check for specific conditions. If a condition exists, you do something. You use if statements frequently with goto statements.

The basic syntax of the command is

If condition  command [else  command ]

As a simple example, you can use the following if statement in a batch file:

if "%date%" == "Tue 11/20/2012" call magic.bat else Echo "Not yet"

The condition of the if command evaluates to either true or false. If the condition is true, it performs the command. If the condition is false, it does not perform the command. If an else clause is included, it is performed if the condition is false. In this example, the condition is a check to see whether today (%date%) is Tuesday, Nov 20, 2012. If so, it calls a batch file named magic.bat.

Although you can enter the entire if command on the same line, it is sometimes easier to read and understand when entered on separate lines. However, if you’re using multiple lines, you must use parentheses around certain areas.

if condition (
  command
) else (
  command )

For example, the if command shown earlier would look like this:

if "%date%" == "Tue 11/16/2010" (
   call magic.bat
) else (
   echo "Not yet"
   )

There are certain conditions you can use, as shown in the following table.

Condition	Example	Comments
Exist	if exist log.txt copy log.txt archive.txt	Checks for the existence of the log.txt file and if it is there, it copies it to the archive.txt file.
Errorlevel	if errorlevel 4 goto eof This assumes a label of :eof exists in the batch file.	Checks for the value of the %errorlevel% variable. If the value is 4, the batch goes to the eof label and presumably ends. It’s common to use this check to redirect the order of the batch file processing with the goto statement.
string comparison string1==string2	if %1 == Yes echo "User entered Yes"	Checks the value of one string against another. Notice that two equal signs (==) are required.
not	if not exist log.txt copy log.txt archive.txt if not errorlevel 4 goto end if not %1 == Yes echo "User did not enter Yes"	The not condition negates the result of the conditional check. If the check results in true, the not condition changes it to false. If the check results in false, the not condition changes it to true.

Note

You can use any valid command that you want after the condition. In other words, you aren’t limited to using only certain commands when you use certain conditions. If it’s a valid command from the command line, it’s a valid command in the if statement.

When using comparison operators, you have several to choose from, as shown in the following table.

Comparison Operator	Remarks
== if string1 == string2 if abc == abc if %1 == abc if %1 == %myvar%	Evaluates to true if string1 and string2 are the same. These values can be literal strings or batch variables, such as %1 or %myvar%. You do not need to enclose literal strings in quotation marks. For example, you can check to see what the user entered as a parameter using %1, and even check to see whether it’s equal to a variable you created with a statement such as set myvar= abc.
if /i string1 ==string2	If you want to ignore the case of the two strings, use the /i switch immediately after the if statement.
equ if value1 equ value2	Equal to. Evaluates to true if the two values are equal.
neq if value1 neq value2	Not equal to. Evaluates to true if the two values are not equal.
lss if value1 lss value2	Less than. Evaluates to true if value1 is less than value2.
leq if value1 leq value2	Less than or equal to. Evaluates to true if value1 is less than or equal to value2.
gtr if value1 gtr value2	Greater than. Evaluates to true if value1 is greater than value2.
geq if value1 geq value2	Greater than or equal to. Evaluates to true if value1 is greater than or equal to value2.

It’s common to use if statements in combination with goto statements and labels. For example, the batch file can accept an input and then check for the value of the input. Based on the input, it can take one of several actions. The following sample shows how to do this accepting a single parameter as %1:

@echo off
if %1#==# goto null
if %1==1 goto sync
if %1==2 goto show
if %1==3 goto summary
if %1 gtr 3 goto outofrange
:Null
echo "No Command entered."
goto eof
:outofrange
echo "Only values 1, 2, and 3 are valid."
goto eof
:sync
repdmin /syncall
:show
repadmin /showrepl
:summary
repadmin /replsummary
:eof

You can enter all of these commands in a batch file named repl.bat. You can then start the batch file with repl 1 (to run repladmin /syncall), repl 2 (to run repadmin /showrepl), or repl 3 (to run repadmin /replsummary).

For clarification, the commands used in the previous batch file are explained in the following table.

Note

Even though the example shows only one command in each of the labels, you can have as many commands as you like.

Batch File Command	Comments
@echo off	Turns off echo so that the batch file commands don’t show.
if %1#==# goto null	Checks for a null value. In other words, if the batch file is entered without a parameter, this evaluates to true and the batch file goes to the :null label.
if %1==1 goto sync if %1==2 goto show if %1==3 goto summary if %1 gtr 3 goto outofrange	Checks for the value of the input. If it is any number, it uses the goto statement to process the command.
:null echo "No Command entered." goto eof	The :null label provides feedback if a parameter isn’t provided. It gives feedback to the user and goes to the end of the file.
:outofrange echo "Only values 1, 2, and 3 are valid." goto eof	The :outofrange label provides feedback on valid numbers. If a value greater than 3 is entered, it gives feedback to the user and goes to the end of the file.
:sync repdmin /syncall	The :sync label includes the repadmin /syncall command to force replication of objects between domain controllers (including those in different sites).
:show repadmin /showrepl	The :show label includes the repadmin /showrepl command, which shows key information on replication.
:summary repadmin /replsummary	The :summary label includes the repadmin /replsummary command, which includes a summary of replication events.
:eof	The :eof file label is placed at the end of the file and doesn’t have any commands after it. The batch file then exits.