Command @
Description Do not
echo this line.
Syntax @
command line
Typical Use To hide
a single line if echo is switched on, or to hide the switching off of the echo
command.
Example echo
This line will be echoed twice to the screen,
@echo Whereas this line will occur only once.
Command ECHO
Description The
ECHO command has several different uses. MS DOS batch files use two echo
'modes'. The default echo mode is ECHO
ON
As well as the echo modes, the ECHO command is used to print
a message to the user. Messages are displayed to the user by preceding a line
of text with ECHO.
Syntax ECHO
MODE ON : ECHO ON
ECHO MODE OFF : ECHO OFF
DISPLAY A MESSAGE : ECHO message
Typical Use The
command @ECHO OFF is almost always placed at the top of a batch file to switch
off subsequent command echo.
ECHO is also the only way a batch file can communicate
information to a user.
Example @ECHO
OFF
ECHO Please insert a disk in drive A: and press any key when
ready.
Command REM
(short for remark)
Description REM is
the MS DOS batch file method of providing comments. Comments are lines of code
which are not executed by the batch file, but rather are used to convey
information about the workings of the batch file itself. Good batch file
programming practice demands a comment at the head of every batch file
explaining its use and syntax. Comments can also be put in other parts of the
file to clarify ambiguous commands and to 'comment-out' a line of commands so
that they are temporarily ignored by the batch file.
Syntax REM
line containing comment.
Typical Use REM
should be used at the top of every batch file to provide a description and
example use. However, too many REM lines are not an example of good programming
style! Don't provide a comment for obvious commands - only the tricky ones!
Example REM
SFORMAT.BAT : Safe Format
REM
REM This batch file implements a safe version of the format
command.
REM The C: drive can not be formatted with this command.
Command PAUSE
Description The
PAUSE command prints the message "Press any key to continue..." to
the screen and waits for the user to respond.
Syntax PAUSE
(it's as simple as that!)
Typical Use The
PAUSE command was the only method of getting a user's response in batch files
until the choice command arrived in MS DOS 6.x. By issuing instructions with
the ECHO command, the PAUSE command waited for the user to read them and
respond appropriately.
Example ECHO
Please insert the disk in drive A: and
PAUSE
Command GOTO
Description The
GOTO command allows a batch file to branch to a different location to continue
executing commands from. To tell the batch file where to go to, a label is
placed after the GOTO command. This label must conform to several guidelines
for it to be a valid batch file label.
Syntax GOTO
label
Typical Use Until
MS DOS 6.x introduced the FOR command, the GOTO command was a batch files only
mechanism of performing a command repeatedly. GOTOs are still the only method
in a batch file to perform a sub-set of commands. (MS DOS Batch files do not
have sub-procedures)
Example IF %1
== "" GOTO ERROR
Command IF
Description The IF
command is used in batch files to test whether a condition is met or not. This
allows the batch file to perform a particular action only if a particular
condition is met. There are several different variations of the IF command: IF
EXIST, IF ERRORLEVEL, and IF x == y (yes! it does use two equal signs!)
Syntax IF
EXIST filename or dirname : used to test for the existance of a file or
directory in MS DOS. This test will return true if the file does exist.
IF ERRORLEVEL : After a program has finished executing in MS
DOS it returns a value to the operating system indicating its success or
failure. This value is stored in the variable ERRORLEVEL. By testing this
variable, a batch file can deduce the result of the program that just finished
running.
IF x == y : This version of the IF statement tests two
string values. If string x is equal to string y this test is evaluated to be
true, otherwise false.
All of the above IF statements can also be negated with the
NOT command. For example -:
IF NOT EXIST filename : Tests to see if the file doesn't
exist. This test will return true if the file doesn't exist.
Typical Use The IF
statement is one of the most useful batch file commands, and as such is
probably the most common. The IF EXIST command is used to check if a file
exists before it is copied/moved/opened/etc. The IF ERRORLEVEL allows a batch
file to check the return value of another program. The IF STRING1 == STRING2 is
commonly used to validate command-line parameters.
Example IF NOT
EXIST %1 MKDIR %1
IF ERRORLEVEL 2 GOTO END
IF %1 == "" GOTO ERROR
Command SHIFT
Description The
SHIFT command is possibly, at first, the most confusing batch file command. It
needn't be. Simply, the SHIFT command increases the number of command-line
parameters accessable by a batch file. Each time SHIFT is called, the value in
the 1st parameter is discarded and replaced by the value of the 2nd parameter.
The value in the 2nd parameter is replaced by the value in the 3rd parameter,
etcetera, etcetera, until the 9th parameter is replaced by the previously
unavailable 10th parameter.
Syntax SHIFT
Typical Use The
SHIFT command provides considerable power to batch files. It allows a batch
file to operate on an unknown number of parameters. The SHIFT command is often
used in situations where an operation needs to be performed on several files or
directories.
Example The following
example displays the contents of the files typed after the batch file name one
page at a time.
:LOOP
TYPE %1 | MORE
SHIFT
IF "%1" == "" GOTO END
GOTO LOOP
:END
Command CALL
Description The
CALL command is used to run another batch file from within a batch file.
Execution of the current batch file is paused and the called batch file is run.
After the called batch file has finished running, the original batch file is
resumed at the line after the CALL statement.
Note: If another batch file is run from within a batch file
by simply using its name, after the called batch file finishes executing,
control is returned to the Command Line, NOT the original batch file.
Syntax CALL
batchfilename [parameters] [switches]
Typical Use The
CALL command is used to provide modularity to batch files. Batch files can be
re-used effortlessly if they are written with modularity in mind.
Example IF %1
== A: CALL FLOPPY.BAT
Command FOR
Description The
FOR command was an invaluable addition to the DOS Batch File Command suite. FOR
repeats a command for a number of files, directories, or text-strings.
Syntax FOR
variable IN list DO command [parameters] [switches]
Where -:
variable is
substituted for each element in the list and passed to command. Variable has a
special format in batch files.
list is a list of
filenames (wildcards allowed), directory names, or text-strings that are to be
processed by command one at a time.
command is a DOS
internal or external command to be performed for each element of the list.
Typical Use The FOR
command performs the same command for each element of a list. Prior to its
introduction, the same effect had to be achieved with GOTOs and IFs, which were
messy and sometimes difficult to follow. Use a FOR to do any necessary looping
in your batch files.
Example The
following is an implementation of the same example presented in the SHIFT
example of displaying many files to the screen with MORE.
FOR %%f IN (*.*) DO TYPE %%f | MORE
A lot neater, huh?!
Command CHOICE
Description The
CHOICE command is perhaps the best addition to MS DOS Batch File commands.
CHOICE makes it possible to accept various user-responses. Before now, users
were presented with crude either/or choices in batch files. The CHOICE command
allows a batch file to detect a users choice from a lits of options.
Syntax CHOICE
[/C:choices] [/N] [/S] [/T:choice,timeout] [TEXT]
Where -:
/C:choices :
specifies the choices that the user can choose from. The choices can only be
single characters.
/N : Do not
display choices and the '?' at the end of the TEXT prompt.
/S : Treat the
choices as case sensitive, meaning that 'a' is a different choice from 'A'. By
default, case is not sensitive - 'a' is equivalent to 'A'.
/T:choice,timeout
: Default to choice after timeout seconds.
TEXT : The text to
display as the prompt of the choice.
Typical Use The
CHOICE command has its obvious use in batch files. It is now possible to easily
get a users response, thus allowing batch files to be much more interactive,
and therefore more useful.
Example The
following batch file snippet displays a simple menu (without a question-mark at
the end of the prompt) and prompts for the users choice, defaulting to option 2
after 5 seconds :
ECHO 1. MS-DOS Editor.
ECHO 2. MS-Windows. (default)
ECHO 3. Defrag the hard-drive.
ECHO 4. Quit.
CHOICE /C:1234 /N /T:2,5 Please choose a menu option.
IF ERRORLEVEL == 4 GOTO QUIT_MENU
IF ERRORLEVEL == 3 GOTO DEFRAG_HD
IF ERRORLEVEL == 2 GOTO RUN_WIN
IF ERRORLEVEL == 1 GOTO RUN_EDIT
:RUN_EDIT
CALL EDIT
:RUN_WIN
CALL WIN
:DEFRAG_HD
DEFRAG c:
:QUIT_MENU
ECHO Safe to switch off machine now...
No comments:
Post a Comment