Dos Batch Read File Line by Line

Script file for Microsoft computer operating systems

Batch file

Filename extensions	.bat, .cmd, .btm
Internet media type	application/bat application/x-bat application/x-msdos-program text/manifestly
Type of format	Scripting
Container for	Scripts

A batch file is a script file in DOS, OS/two and Microsoft Windows. Information technology consists of a series of commands to be executed past the command-line interpreter, stored in a plain text file. A batch file may incorporate any command the interpreter accepts interactively and utilize constructs that enable conditional branching and looping within the batch file, such as IF, FOR, and GOTO labels. The term "batch" is from batch processing, meaning "non-interactive execution", though a batch file might non process a batch of multiple data.

Similar to Job Control Language (JCL), DCL and other systems on mainframe and minicomputer systems, batch files were added to ease the work required for sure regular tasks by allowing the user to set up up a script to automate them. When a batch file is run, the shell programme (usually Command.COM or cmd.exe) reads the file and executes its commands, unremarkably line-by-line.^[i] Unix-like operating systems, such as Linux, have a similar, but more flexible, type of file called a vanquish script.^[2]

The filename extension .bat is used in DOS and Windows. Windows NT and OS/2 likewise added .cmd. Batch files for other environments may take dissimilar extensions, e.thousand., .btm in 4DOS, 4OS2 and 4NT related shells.

The detailed handling of batch files has changed significantly between versions. Some of the detail in this article applies to all batch files, while other details apply only to certain versions.

Variants [edit]

DOS [edit]

In DOS, a batch file can exist started from the command-line interface by typing its name, followed by any required parameters and pressing the ↵ Enter key. When DOS loads, the file AUTOEXEC.BAT, when present, is automatically executed, so any commands that need to be run to set the DOS environment may exist placed in this file. Estimator users would have the AUTOEXEC.BAT file gear up upwardly the system engagement and time, initialize the DOS environment, load whatever resident programs or device drivers, or initialize network connections and assignments.

A .bat file name extension identifies a file containing commands that are executed by the command interpreter COMMAND.COM line by line, equally if it were a list of commands entered manually, with some extra batch-file-specific commands for bones programming functionality, including a GOTO command for changing flow of line execution.

Early Windows [edit]

Microsoft Windows was introduced in 1985 as a graphical user interface-based (GUI) overlay on text-based operating systems and was designed to run on DOS. In order to start information technology, the WIN command was used, which could be added to the stop of the AUTOEXEC.BAT file to allow automatic loading of Windows. In the before versions, 1 could run a .bat type file from Windows in the MS-DOS Prompt. Windows three.1x and before, as well as Windows 9x invoked Command.COM to run batch files.

OS/2 [edit]

The IBM OS/two operating system supported DOS-manner batch files. It likewise included a version of REXX, a more than advanced batch-file scripting language. IBM and Microsoft started developing this arrangement, just during the construction of information technology broke upward after a dispute; equally a outcome of this, IBM referred to their DOS-like panel shell without mention of Microsoft, naming it but DOS, although this seemingly fabricated no difference with regard to the way batch files worked from Control.COM.

Os/2'due south batch file interpreter also supports an EXTPROC command. This passes the batch file to the program named on the EXTPROC file equally a data file. The named program tin exist a script file; this is like to the #! mechanism.

Windows NT [edit]

Unlike Windows 98 and earlier, the Windows NT family of operating systems does not depend on MS-DOS. Windows NT introduced an enhanced 32-bit control interpreter (cmd.exe) that could execute scripts with either the .CMD or .BAT extension. Cmd.exe added additional commands, and implemented existing ones in a slightly different way, and so that the same batch file (with unlike extension) might work differently with cmd.exe and COMMAND.COM. In most cases, operation is identical if the few unsupported commands are not used. Cmd.exe's extensions to Command.COM can exist disabled for compatibility.

Microsoft released a version of cmd.exe for Windows 9x and ME called WIN95CMD to permit users of older versions of Windows to apply certain cmd.exe-mode batch files.

As of Windows viii^[update], cmd.exe is the normal command interpreter for batch files; the older Control.COM tin can exist run every bit well in 32-scrap versions of Windows able to run 16-bit programs.^{[nb i]}

Filename extensions [edit]

.bat

The first filename extension used by Microsoft for batch files. This extension runs with DOS and all versions of Windows, under Command.COM or cmd.exe, despite the dissimilar ways the 2 control interpreters execute batch files.

.cmd

Used for batch files in Windows NT family unit and sent to cmd.exe for interpretation. Control.COM does not recognize this file name extension, then cmd.exe scripts are not executed in the wrong Windows environment by error. In improver, append, dpath, ftype, ready, path, assoc and prompt commands, when executed from a .bat file, alter the value of the errorlevel variable only upon an error, whereas from within a .cmd file, they would affect errorlevel fifty-fifty when returning without an error.^[three] It is also used by IBM'south OS/2 for batch files.

.btm

The extension used past 4DOS, 4OS2, 4NT and Take Command. These scripts are faster, especially with longer ones, as the script is loaded entirely ready for execution, rather than line-by-line.^[4]

Batch file parameters [edit]

Command.COM and cmd.exe support special variables (%0, %ane through %9) in order to refer to the path and name of the batch task and the starting time nine calling parameters from within the batch task, encounter also SHIFT. Non-real parameters are replaced by a nada-length string. They can be used similar to surround variables, but are not stored in the surroundings. Microsoft and IBM refer to these variables as replacement parameters or replaceable parameters, whereas Digital Research, Novell and Caldera established the term replacement variables ^[v] for them. JP Software calls them batch file parameters.^[6]

Examples [edit]

This example batch file displays Hi Globe!, prompts and waits for the user to press a key, and so terminates. (Notation: Information technology does not matter if commands are lowercase or capital unless working with variables)

                        @            Echo            OFF            Echo            Hello World!            PAUSE          

To execute the file, it must be saved with the filename extension suffix .bat (or .cmd for Windows NT-type operating systems) in plain text format, typically created past using a text editor such equally Microsoft Notepad or a discussion processor working in manifestly text mode.

When executed, the following is displayed:

Hello Globe! Press whatever key to go on . . .        

Explanation [edit]

The interpreter executes each line in turn, starting with the first. The @ symbol at the starting time of whatever line prevents the prompt from displaying that control as information technology is executed. The command ECHO OFF turns off the prompt permanently, or until it is turned on once again. The combined @ECHO OFF is oft every bit hither the first line of a batch file, preventing any commands from displaying, itself included. Then the next line is executed and the Repeat Hello World! command outputs How-do-you-do Globe!. The next line is executed and the PAUSE command displays Press any key to continue . . . and pauses the script's execution. Later a key is pressed, the script terminates, as there are no more commands. In Windows, if the script is executed from an already running command prompt window, the window remains open at the prompt as in MS-DOS; otherwise, the window closes on termination.

Limitations and exceptions [edit]

Zilch values in variables [edit]

Variable expansions are substituted textually into the command, and thus variables which contain nothing simply disappear from the syntax, and variables which contain spaces turn into multiple tokens. This can lead to syntax errors or bugs.

For example, if %foo% is empty, this argument:

parses as the erroneous construct:

Similarly, if %foo% contains abc def, and then a different syntax error results:

                        IF            abc              def            ==bar            ECHO            Equal          

The usual way to prevent this problem is to surround variable expansions in quotes and then that an empty variable expands into the valid expression IF ""=="bar" instead of the invalid IF ==bar. The text that is existence compared to the variable must also be enclosed in quotes, because the quotes are non special delimiting syntax; these characters represent themselves.

                        IF            "            %foo%            "            ==            "bar"            Repeat            Equal          

The delayed !VARIABLE! expansion available in Windows 2000 and later may be used to avoid these syntactical errors. In this case, zero or multi-word variables do non fail syntactically considering the value is expanded after the IF command is parsed:

Another difference in Windows 2000 or higher is that an empty variable (undefined) is not substituted. As described in previous examples, previous batch interpreter behaviour would take resulted in an empty string. Example:

                        C:\>            set up            MyVar            =            C:\>            echo            %MyVar%            %MyVar%            C:\>            if            "            %MyVar%            "            ==            ""            (            echo            MyVar is not defined)            else            (            echo            MyVar is            %MyVar%            )            MyVar is %MyVar%          

Batch interpreters prior to Windows 2000 would have displayed event MyVar is non defined.

Quotation marks and spaces in passed strings [edit]

Different Unix/POSIX processes, which receive their command-line arguments already dissever up past the beat out into an array of strings, a Windows process receives the unabridged command-line as a single string, via the GetCommandLine API function. As a result, each Windows application can implement its own parser to dissever the entire command line into arguments. Many applications and command-line tools have evolved their own syntax for doing that, and so there is no single convention for quoting or escaping metacharacters on Windows command lines.

• For some commands, spaces are treated as delimiters that divide arguments, unless those spaces are enclosed by quotation marks. Diverse conventions exist of how quotation marks can be passed on to the application:
  • A widely used convention is implemented by the command-line parser built into the Microsoft Visual C++ runtime library in the CommandLineToArgvW function. It uses the convention that 2n backslashes followed by a quotation marking (") produce n backslashes followed past a begin/end quote, whereas (2north)+1 backslashes followed by a quotation mark once more produce n backslashes followed by a quotation marking literal. The same convention is role of the .NET Framework specification.^[7]
    • An undocumented aspect is that "" occurring in the middle of a quoted string produces a single quotation mark.^[7] (A CRT modify in 2008 [msvcr90] modified this undocumented treatment of quotes.^[8]) This is helpful for inserting a quotation mark in an argument without re-enabling interpretation of cmd metacharacters like |, & and >. (cmd does not recognize the usual \" as escaping the quote. Information technology re-enables these special meanings on seeing the quote, thinking the quotation has ended.)
  • Another convention is that a single quotation mark (") is non included as part of the string. Notwithstanding, an escaped quotation mark (""") can be part of the string.^{[ commendation needed ]}
  • Yet another common convention comes from the use of Cygwin-derived ported programs. Information technology does not differentiate between backslashes occurring before or not earlier quotes. Come across glob (programming) § Windows and DOS for information on these culling control-line parsers.^[9]
  • Some important Windows commands, similar cmd.exe and wscript.exe, utilise their own rules.^[8]
• For other commands, spaces are not treated equally delimiters and therefore practice not demand quotation marks. If quotes are included they become office of the string. This applies to some built-in commands similar echo.

Where a cord contains quotation marks, and is to be inserted into another line of text that must also exist enclosed in quotation marks, particular attention to the quoting mechanism is required:

                        C:\>            set            foo            =            "this string is enclosed in quotation marks"            C:\>            repeat            "test ane                        %foo%            "            "test ane "this string is enclosed in quotation marks""            C:\>eventcreate /T Warning /ID 1 /L System /SO            "Source"            /D            "Case:                        %foo%            "            Fault: Invalid Argument/Option - 'string'.            Type "EVENTCREATE /?" for usage.          

On Windows 2000 and afterwards, the solution is to supplant each occurrence of a quote character within a value by a serial of three quote characters:

                        C:\>            set            foo            =            "this cord is enclosed in quotes"            C:\>            fix            foo            =            %foo:"="""%            C:\>            echo            "examination i                        %foo%            "            "exam ane """this string is enclosed in quotes""""            C:\>eventcreate /T Warning /ID 1 /L System /SO            "Source"            /D            "Example:                        %foo%            "            SUCCESS: A 'Warning' type upshot is created in the 'Source' log/source.          

Escaped characters in strings [edit]

Some characters, such as pipage (|) characters, accept special meaning to the command line. They cannot be printed as text using the Repeat control unless escaped using the caret ^ symbol:

                        C:\>            Repeat            foo            |            bar            'bar' is not recognized as an internal or external command,            operable program or batch file.            C:\>            Echo            foo            ^|            bar            foo | bar          

However, escaping does non work as expected when inserting the escaped grapheme into an environment variable. The variable ends up containing a live pipe command when simply echoed. It is necessary to escape both the caret itself and the escaped character for the character display every bit text in the variable:

                        C:\>            set            foo            =bar            |            baz            'baz' is not recognized equally an internal or external command,            operable program or batch file.            C:\>            set            foo            =bar            ^|            baz            C:\>            echo            %foo%            'baz' is not recognized as an internal or external command,            operable plan or batch file.            C:\>            set up            foo            =bar            ^^^|            baz            C:\>            echo            %foo%            bar | baz          

The delayed !VARIABLE! expansion available with CMD /5:ON or with SETLOCAL ENABLEDELAYEDEXPANSION in Windows 2000 and later may be used to bear witness special characters stored in environment variables because the variable value is expanded later on the control was parsed:

                        C:\>cmd /Five:ON            Microsoft Windows [Version 6.i.7601]            Copyright (c) 2009 Microsoft Corporation. All rights reserved.            C:\>            set            foo            =bar            ^|            baz            C:\>            echo            !foo!            bar | baz          

Sleep or scripted delay [edit]

Until the TIMEOUT command was introduced with Windows Vista, there was no easy way to implement a timed break, equally the Interruption command halts script activity indefinitely until whatever primal is pressed.

Many workarounds were possible,^[10] but generally only worked in some environments: The CHOICE command was not available in older DOS versions, PING was only available if TCP/IP was installed, and then on. No solution was available from Microsoft, but a number of pocket-size utility programs, could be installed from other sources. A commercial instance would be the 1988 Norton Utilities Batch Enhancer (BE) control, where Exist Delay 18 would wait for one second, or the free 94-byte WAIT.COM^[11] where Look 5 would expect for five seconds, and then return command to the script. Most such programs are 16-bit .COM files, and so are incompatible with 64-scrap Windows.

Text output with stripped CR/LF [edit]

Usually, all printed text automatically has the control characters for carriage render (CR) and line feed (LF) appended to the end of each line.

• batchtest.bat

                                          C:\>batchtest.bat                    foo                    bar                  

It does not affair if the ii echo commands share the same command line; the CR/LF codes are inserted to pause the output onto split up lines:

                        C:\>            @            repeat            Message 1&@            echo            Bulletin two            Message one            Message two          

A play a joke on discovered with Windows 2000 and later is to use the special prompt for input to output text without CR/LF trailing the text. In this example, the CR/LF does not follow Message 1, but does follow Line 2 and Line three:

• batchtest2.bat

                                          @                    repeat                    off                    set                    /p                    =                    "Message one"                    <nul                    echo                    Message 2                    echo                    Message three                  

                                          C:\>batchtest2.bat                    Message 1Message 2                    Message 3                  

This can be used to output data to a text file without CR/LF appended to the finish:

                        C:\>            set up            /p            =            "Message 1"            <nul            >information.txt            C:\>            set            /p            =            "Bulletin ii"            <nul            >>data.txt            C:\>            set            /p            =            "Bulletin 3"            <nul            >>data.txt            C:\>            type            data.txt            Message 1Message 2Message 3          

Nevertheless, there is no way to inject this stripped CR/LF prompt output direct into an surroundings variable.

Setting a Compatible Naming Convention (UNC) working directory from a shortcut [edit]

Information technology is not possible to have a control prompt that uses a UNC path as the current working directory; due east.1000. \\server\share\directory\

The command prompt requires the utilize of drive letters to assign a working directory, which makes running complex batch files stored on a server UNC share more difficult. While a batch file can be run from a UNC file path, the working directory default is C:\Windows\System32\.

In Windows 2000 and later, a workaround is to use the PUSHD and POPD command with command extensions.^{[nb ii]}

If not enabled by default, command extensions tin can exist temporarily enabled using the /E:ON switch for the command interpreter.

So to run a batch file on a UNC share, assign a temporary drive alphabetic character to the UNC share, and apply the UNC share equally the working directory of the batch file, a Windows shortcut can be constructed that looks like this:

• Target: %COMSPEC% /E:ON /C "PUSHD """\\SERVER\SHARE\DIR1\DIR2\""" & BATCHFILE.BAT & POPD"

The working directory attribute of this shortcut is ignored.

This besides solves a problem related to User Account Control (UAC) on Windows Vista and newer. When an administrator is logged on and UAC is enabled, and they try to run a batch file as administrator from a network drive letter, using the correct-click file context carte, the operation will unexpectedly neglect. This is considering the elevated UAC privileged account context does not have network bulldoze letter of the alphabet assignments, and it is non possible to assign drive letters for the elevated context via the Explorer beat or logon scripts. Withal, by creating a shortcut to the batch file using the in a higher place PUSHD / POPD construct, and using the shortcut to run the batch file as ambassador, the temporary drive alphabetic character volition be created and removed in the elevated business relationship context, and the batch file will function correctly.

The post-obit syntax does correctly expand to the path of the current batch script.

%~dp0        

UNC default paths are turned off by default as they used to crash older programs.^[12]

The Dword registry value DisableUNCCheck at HKEY_CURRENT_USER\Software\Microsoft\Command Processor ^[12] allows the default directory to exist UNC. CD command will turn down to change but placing a UNC path in Default Directory in a shortcut to Cmd or by using the Beginning command. start "" /d \\127.0.0.1\C$ "cmd /k" (C$ share is for administrators).

Character set [edit]

Batch files employ an OEM character gear up, as defined by the reckoner, due east.g. Code page 437. The non-ASCII parts of these are incompatible with the Unicode or Windows graphic symbol sets otherwise used in Windows so care needs to be taken.^[13] Non-English file names work only if entered through a DOS graphic symbol set compatible editor. File names with characters exterior this set do not piece of work in batch files.

To become output in Unicode into file pipes from an internal control such every bit dir, one tin use the cmd /U command. For example, cmd /U /C dir > files.txt creates a file containing a directory listing with correct Windows characters, in the UTF-16LE encoding.

Batch viruses and malware [edit]

As with any other programming language, batch files can be used maliciously. Simple trojans and fork bombs are easily created, and batch files can practise a class of DNS poisoning by modifying the hosts file. Batch viruses are possible, and tin too spread themselves via USB wink drives by using Windows' Autorun capability.^[14]

The following control in a batch file will delete all the data in the current directory (binder) - without first asking for confirmation:

These three commands are a elementary fork bomb that will continually replicate itself to deplete bachelor system resources, slowing down or crashing the system:

                        :            Pinnacle            start            ""            %0            goto            TOP          

Other Windows scripting languages [edit]

The cmd.exe control processor that interprets .cmd files is supported in all 32- and 64-bit versions of Windows up to at to the lowest degree Windows 10^[update]. COMMAND.EXE, which interprets .BAT files, was supported in all 16- and 32-bit versions up to at least Windows ten.^{[nb 3]}

There are other, afterward and more powerful, scripting languages available for Windows. However, these require the scripting language interpreter to be installed earlier they tin be used:

• KiXtart (.kix) — developed past a Microsoft employee in 1991, specifically to see the demand for commands useful in a network logon script while retaining the simple 'feel' of a .cmd file.
• Windows Script Host (.vbs , .js and .wsf) — released by Microsoft in 1998, and consisting of cscript.exe and wscript.exe, runs scripts written in VBScript or JScript. It can run them in windowed mode (with the wscript.exe host) or in console-based fashion (with the cscript.exe host). They have been a part of Windows since Windows 98.
• PowerShell (.ps1) — released in 2006 by Microsoft and can operate with Windows XP (SP2/SP3) and later versions. PowerShell tin can operate both interactively (from a control-line interface) and likewise via saved scripts, and has a strong resemblance to Unix shells.^[xv]
• Unix-fashion shell scripting languages can exist used if a Unix compatibility tool, such as Cygwin, is installed.
• Cantankerous-platform scripting tools including Perl, Python, Ruby, Rexx, Node.js and PHP are available for Windows.

Script files run if the filename without extension is entered. There are rules of precedence governing interpretation of, say, DoThis if DoThis.com, DoThis.exe, DoThis.bat, DoThis.cmd, etc. exist; by default DoThis.com has highest priority. This default gild may be modified in newer operating systems past the user-settable PATHEXT environs variable.

See too [edit]

• Listing of DOS commands

Notes [edit]

1. ^ To verify that Control.COM remains available (in the \WINDOWS\SYSTEM32 directory), type COMMAND.COM at the 32-bit Windows 7 command prompt.
2. ^ "If Command Extensions are enabled the PUSHD command accepts network paths in add-on to the normal drive letter and path. If a network path is specified, PUSHD creates a temporary drive letter that points to that specified network resource and and so change the current bulldoze and directory, using the newly defined drive letter. Temporary drive letters are allocated from Z: on down, using the first unused drive letter found." --The help for PUSHD in Windows seven
3. ^ Availability of CMD.EXE and COMMAND.COM tin can be confirmed by invoking them in whatever version of Windows (COMMAND.COM not in 64-fleck versions; probably only available in Windows viii 32-bit versions if installed with option to support 16-bit programs).

References [edit]

1. ^ "Using batch files: Scripting; Management Services". Technet.microsoft.com. 2005-01-21. Retrieved 2012-11-xxx .
2. ^ Henry-Stocker, Sandra (2007-07-18). "Use your Unix scripting skills to write a batch file". itworld.com. IT Earth. Retrieved 2018-06-13 .
3. ^ "Difference betwixt bat and cmd | WWoIT - Wayne'south Globe of IT". waynes-world-it.blogspot.fr. 2012-eleven-xv. Retrieved 2012-11-30 .
4. ^ "btm file extension :: all about the .btm file type". Cryer.co.united kingdom. Retrieved 2012-11-30 .
5. ^ Caldera DR-DOS 7.02 User Guide, Caldera, Inc., 1998 [1993, 1997], archived from the original on 2016-eleven-05, retrieved 2013-08-ten
6. ^ Brothers, Hardin; Rawson, Tom; Conn, Rex C.; Paul, Matthias R.; Dye, Charles E.; Georgiev, Luchezar I. (2002-02-27). 4DOS viii.00 online assist.
7. ^ ^{a b} ".Net Core Runtime: System.Diagnostics.Process.Unix". GitHub . Retrieved 2020-02-11 . Ii consecutive double quotes inside an inQuotes region should event in a literal double quote (the parser is left in the inQuotes region). This behavior is not part of the spec of lawmaking:ParseArgumentsIntoList, but is uniform with CRT and .Internet Framework.
8. ^ ^{a b} Deley, David. "How Command Line Parameters Are Parsed".
9. ^ "Child process documentation, section Windows Command Line, NodeJS PR #29576". GitHub . Retrieved 2020-02-11 .
10. ^ "How to do a delay", ericphelps.com
11. ^ Utilities for DOS, linking to Wait.ZIP (archive of Expect.COM) and other programs
12. ^ ^{a b} https://back up.microsoft.com/en-united states/kb/156276 ^{[ dead link ]}
13. ^ Chen, Raymond. "Proceed your eye on the code folio". Microsoft.
14. ^ http://www.explorehacking.com/2011/01/batch-files-art-of-creating-viruses.html
15. ^ "Windows PowerShell - Unix comes to Windows". Geekswithblogs.net. Retrieved 2012-11-30 .

External links [edit]

• Microsoft Windows XP Batch file reference
• How Windows batch files work
• Windows 10 batch file commands
• FreeDOS' FreeCOM : complete feature list
• Windows Command Line Interface script programming links
• scripting related information (also command line)
• dbenham. "How does the Windows Command Interpreter (CMD.EXE) parse scripts?". Stack Overflow.

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Source: https://en.wikipedia.org/wiki/Batch_file

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