cmd batch use variable

1.define and del variable

　　set variablename=variablevalue_in_string

　   variable name is not case-sensitive, could have embedded spaces, like set test test=t 

      

     if value variablevalue_in_string is emty, the variable is deleted, like set variablename=, then set variablename will show tip that no such variable exists.

2.assign value to variable and del

　　set variablename=variablevalue_in_string

　　set /p variablename=please enter variablename value

set /p is accept use input to a variable

      set /p variablename=<filename.txt

set /p =< will assign first row to a variable

      to avoid your value endwith spaces, you can set "variablename=variablevalue_in_string"       

  

3.dynamic evaluate variable value

      set start=1

      set len=2

      set str=abcdefg 

      call set substr=%%str:~%start%,%len%%%           (%%str:~1,2%% get substring)

      you can pass args to variablevalue_in_string and evaluate the result

4.use/call variable

　　%variablename%   if the variable is not defined, the %variablename% is emtpy:

set first=1

set sum=%first% +2

set sum will be:sum=1+2 

 

      set /a variablename=variablevalue_in_int operator other_variablename like:

set /a first=1 or  set first=1 (when variable first with /a used in arithmetic expression, the value will be translated to number )

set /a sum=2+first

        set sum will be sum=3 

         

5.show variable value

      set virablename             show variable name and value.

　　echo %virablename%     show variable value

4.query variable

　　set    will show all variables and their values in current session of cmd

　　set p will show all matched variables start with "p" and their values in current session of cmd

      if there is no variable matched, the errorlevel will be 1(an error) 

6.variable in number

      set /a variablename=variablevalue_in_int  (a is arithmetic)

      set a=1

      set /a sum=2+a  or       set /a sum=2+%a%

      set sum will be 3 

      

     set variable for hex/octal number set /a a=0x12 or set a=0x12 for hex number, and set /a a=02 set a=02 for octal number     

7.system variable

 The following table lists the system and local environment variables for Windows XP.

Variable	Type	Description
%ALLUSERSPROFILE%	Local	Returns the location of the All Users Profile.
%APPDATA%	Local	Returns the location where applications store data by default.
%CD%	Local	Returns the current directory string.
%CMDCMDLINE%	Local	Returns the exact command line used to start the current Cmd.exe.
%CMDEXTVERSION%	System	Returns the version number of the current Command Processor Extensions.
%COMPUTERNAME%	System	Returns the name of the computer.
%COMSPEC%	System	Returns the exact path to the command shell executable.
%DATE%	System	Returns the current date. Uses the same format as the date /t command. Generated by Cmd.exe. For more information about the datecommand, see Date
%ERRORLEVEL%	System	Returns the error code of the most recently used command. A non zero value usually indicates an error.
%HOMEDRIVE%	System	Returns which local workstation drive letter is connected to the user's home directory. Set based on the value of the home directory. The user's home directory is specified in Local Users and Groups.
%HOMEPATH%	System	Returns the full path of the user's home directory. Set based on the value of the home directory. The user's home directory is specified in Local Users and Groups.
%HOMESHARE%	System	Returns the network path to the user's shared home directory. Set based on the value of the home directory. The user's home directory is specified in Local Users and Groups.
%LOGONSEVER%	Local	Returns the name of the domain controller that validated the current logon session.
%NUMBER_OF_PROCESSORS%	System	Specifies the number of processors installed on the computer.
%OS%	System	Returns the operating system name. Windows 2000 displays the operating system as Windows_NT.
%PATH%	System	Specifies the search path for executable files.
%PATHEXT%	System	Returns a list of the file extensions that the operating system considers to be executable.
%PROCESSOR_ARCHITECTURE%	System	Returns the chip architecture of the processor. Values: x86, IA64.
%PROCESSOR_IDENTIFIER%	System	Returns a description of the processor.
%PROCESSOR_LEVEL%	System	Returns the model number of the processor installed on the computer.
%PROCESSOR_REVISION%	System	Returns the revision number of the processor.
%PROMPT%	Local	Returns the command prompt settings for the current interpreter. Generated by Cmd.exe.
%RANDOM%	System	Returns a random decimal number between 0 and 32767. Generated by Cmd.exe.
%SYSTEMDRIVE%	System	Returns the drive containing the Windows XP root directory (that is, the system root).
%SYSTEMROOT%	System	Returns the location of the Windows XP root directory.
%TEMP% and %TMP%	System and User	Returns the default temporary directories that are used by applications available to users who are currently logged on. Some applications require TEMP and others require TMP.
%TIME%	System	Returns the current time. Uses the same format as the time /t command. Generated by Cmd.exe. For more information about the timecommand, see Time
%USERDOMAIN%	Local	Returns the name of the domain that contains the user's account.
%USERNAME%	Local	Returns the name of the user who is currently logged on.
%USERPROFILE%	Local	Returns the location of the profile for the current user.
%WINDIR%	System	Returns the location of the operating system directory.

copy from:http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/ntcmds_shelloverview.mspx?mfr=true

8.permanent save variable

use setx, like setx a 3,  without =

used after windows 2k3, of course you can download and install it

reference:

http://vlaurie.com/computers2/Articles/environment.htm 

http://www.wilsonmar.com/1envvars.htm 

http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/ntcmds_shelloverview.mspx?mfr=true