MS DOS Command: ASSOC

Reference from Microsoft WinXP cmd help

Description

Displays or modifies file extension associations

Syntax

ASSOC [.ext [=[fileType]]]

Parameters

.ext	Specifies the file extension to associate the file type with
fileType	Specifies the file type to associate with the file extension

Remarks

Specify ASSOC without parameters to display the current file associations.

Specify ASSOC with a file extension only to displays the current file association for that file extension.

Specify ASSOC with nothing for the file type to delete the association for the file extension.

MS DOS Command: XCOPY

Reference from Microsoft WinXP cmd help

Description

Copies files and directory trees.

Syntax

XCOPY source [destination] [/A | /M] [/D[:date]] [/P] [/S [/E]] [/V] [/W] [/C] [/I] [/Q] [/F] [/L] [/G] [/H] [/R] [/T] [/U] [/K] [/N] [/O] [/X] [/Y] [/-Y] [/Z] [/EXCLUDE:file1[+file][+file2][+file3]...]

Parameters

source	Specifies the file(s) to copy.
destination	Specifies the location and/or name of new files.
/A	Copies only files with the archive attribute set, doesnot change the attribute.
/M	Copies only files with the archive attribute set, turns off the archive attribute.
/D:m-d-y	Copies files changed on or after the specified date. If no date is given, copies only those files whose source time is newer
/EXCLUDE:file1[+file][+file2][+file3]...	Specifies a list of files containing strings. Each string should be in a separate line in the files. When any of the strings match any part of the absolute path of the file to be copies, that file will be excluded from being copied. For example, specifying a string like \obj\ or .obj will exclude all files underneath the directory obj or all files with the .obj extension respectively.
/P	Prompts you before creating each destination file.
/S	Copies directories and subdirectories except empty ones.
/E	Copies directories and subdirectories, including empty ones. Same as /S /E. May be used to modify /T.
/V	Verifies each new file.
/W	Prompts you to press a key before copying.
/C	Continues copying even if errors occur.
/I	If destination does not exist and copying more than one file, assumes that destination must be a directory.
/Q	Does not display file names while copying.
/F	Displays full source and destination file names while copying.
/L	Displays files that would be copied.
/G	Allows the copying of encrypted files to destination that does not support encryption.
/H	Copies hidden and system files also.
/R	Overwrites read-only files.
/T	Creates directory structure, but does not copy files. Does not include empty directories or subdirectories. /T /E includes empty directories and subdirectories.
/U	Copies only files that already exist in destination.
/K	Copies attributes. Normal Xcopy will reset read-only attributes.
/N	Copies using the generated short names.
/O	Copies file ownership and ACL information.
/X	Copies file audit settings (implies /O).
/Y	Suppresses prompting to confirm you want to overwrite an existing destination file.
/-Y	Causes prompting to confirm you want to overwrite an existing destination file.
/Z	Copies networked files in restartable mode.

Remarks

The switch /Y may be preset in the COPYCMD environment variable. This may be overridden with /-Y on the command line.

MS DOS Command: SET

Reference from Microsoft WinXP cmd help

Description

Displays ,sets, or removes cmd.exe environment variables.

Syntax

SET [variable=[string]]

Parameters

variable	Specifies the environment-variable name.
string	Specifies a series of characters to assign to the variables.

Remarks

Type SET without parameters to display the current environment variables.

If Command Extensions are enabled SET changes as follows:

SET command invoked with just a variable name, no equal sign or value will display the value of all variables whose prefix matches the name given to the SET command. For example:

SET P

would display all variables that begin with the letter 'P'

SET command will set the ERRORLEVEL to 1 if the variable name is not found in the current environment.

SET command will not allow an equal sign to be part of the name of a variable.

Two new switches have been added to the SET command:

SET /A expression

SET /P variable=[promptString]

The /A switch specifies that the string to the right of the equal sign is a numerical expression that is evaluated. The expression evaluator is pretty simple and supports the following operations, in decreasing order of precedence:

()	grouping
! ~ _:-	unary operators
* / %	arithmetic operators
+ -	arithmetic operators
<< >>	logical shift
&	bitwise and
^	bitwise exclusive or
|	bitwise or
= *= /= %= += -= &= ^= |= <<= >>=	assignment
,	expression separator

If you use any of the logical or modulus operators, you need to enclose the expression string in quotes. Any non-numeric strings in the expression are treated as environment variable names whose values are converted t numbers before using them. If an environment variable name is specified but is not defined in the current environment, then a value of zero is used. This allows you to do arithmetic with environment variable values without having to type all those % signs to get their values.

If SET /A is executed from the command line outside of a command script, then it displays the final value of the expression. The assignment operator requires an environment variable name to the left of the assignment operator. Numeric values are decimal numbers, unless prefixed by 0x for hexadecimal numbers, and 0 for octal numbers. So 0x12 is the same as 18 isthe same as 022. Please note that the octal notation can be confusing:08 and 09 are not valid numbers 8 and 9 are not valid octal digits.

The /P switch allows you to set the value of a variable to a line of input entered by the user. Displays the specified promptString before reading the line of input. The promptString can be empty.

Environment variable substitution has been enhanced as follows:

%PATH:str1=str2%

would expand the PATH environment variable, substituting each occurrence of "str1" in the expanded result with "str2". "str2" can be empty string to effectively delete all occurrences of "str1" from the expanded output. "str1" can begin with an asterisk, in which case it will match everything from the beginning of the expanded output to the first occurrence of the remaining portion of str1.

May also specify substrings for an expansion.

%PATH:~10,5%

would expand the PATH environment variable, and then use only the 5 characters that begin at the 11th (offset 10) character of the expanded result. If the length is not specified, then it defaults to the reminder of thevariable value. If either number (offset or length) is negative, then the number used is the length of the environment variable value added to the offset or length specified.

%PATH:~-10%

would extract the last 10 characters of the PATH variable.

%PATH:~0,-2%

would extract all but the last 2 characters of the PATH variable.

Finally, support for delayed environment variable expansion has beed added. This support is alway disabled by default, but may be enabled/disabled via the /V command line switch to CMD.EXE.

Delayed environment variable expansion is useful for gettign around the limitations of the current expansion which happens when a line of text is read, not when it is executed. The following example demonstrates the problem with immediate variable expansion:

set VAR=before

if "%VAR%" == "before" (

; set VAR=after

if "%VAR%" == "after" @echo If you see this, it worked

)

would never display the message, since the %VAR% in BOTH IF statements is substituted when the first IF statement is read, since it logically includes the body of the IF, which is a command statement. So the IF inside the compound statement is really comparing the "before" with "after" wihich will never be equal.

Similarly, the following example will not work as expected:

set LIST=

for %i in (*) do set LIST=%LST% %i

echo %LIST%

in that it will NOT build up a list of files in the current directory, but instead will just set the LIST variable to the last file found. Again, this is because the %LIST% is expanded just once when the FOR statement is read, and at that time the LIST variable is empty.

So the actual FOR loop we are executing is:

for %i in (*) do set LIST= %i

which just keeps setting LIST to the last file found.

Delayed environment variable expansion allows you to use a different character (the exclamation mark) to expand environment variables at execution time. If delayed variable expansion is enabled, the above examples could be written as follows to work as intended:

set VAR=before

if "%VAR%" == "before" (

set VAR=after

if "!VAR!" == "after" @echo If you see this, it worked

)

  

set LIST=

for %i in (*) do set LIST=!LST! %i

echo %LIST%

If Command Extensions are enabled, then there are several dynamic environment variables that can be expanded but which donot show up in the list of variables displayed by SET. These variable values are computed dynamically each time the value of the variable is expanded. If the user explicitly defines a variable with one of these names, then that definition will override the dynamic one described below:

%CD%	expands to the current directory string.
%DATE%	expands to current date using same format as DATE command.
%TIME%	expands to current time using same format as TIME command.
%RANDOM%	expands to a random decimal number between 0 and 32767.
%ERRORLEVEL%	expands to the current ERRORLEVEL value.
%CMDEXTVERSION%	expands to the current Command Processor Extensions version number.
%CMDCMDLINE%	expands to the original command line that invoked the Command Processor.