Parameters are most often separated by spaces, but any of the following are also valid delimiters:. This is because batch file parameters are passed to CMD. Adding the escape character before a command symbol allows it to be treated as ordinary text.
The Command shell was the first shell built into Windows to automate routine tasks, like user account management or nightly backups, with batch.
With Windows Script Host, you could run more sophisticated scripts in the Command shell. For more information, see cscript or wscript. You can perform operations more efficiently by using scripts than you can by using the user interface.
Scripts accept all commands that are available at the command line. PowerShell was designed to extend the capabilities of the Command shell to run PowerShell commands called cmdlets. Cmdlets are similar to Windows Commands but provide a more extensible scripting language. A reference of exit and error codes for Windows Commands can be found in the Debug system error codes articles that may be helpful to understanding errors produced.
You can configure the Command shell to automatically complete file and directory names on a computer or user session when a specified control character is pressed. The batch file first passes the starting directory to the program, then generates a list of subdirectories which it also passes one at a time to the program.
Our batch file faithfully quotes each directory in case it contain spaces. Once in a while the script neglects to process files in the starting directory.
We discover that it fails whenever the user appends a trailing backslash to the specified directory. The backslash is interpreted by CreateDocs as an escape for the closing double quote.
Someone will get it wrong! To fix this in CreateDocs would require some relatively complex logic. Then one day we change our build process. We want to be able to debug using binaries built on different development machines. We could fix this various ways, but we decide to use a fixed drive letter in the build scripts and use subst to map the root of the source code tree, wherever it is on a particular machine, to the root of this drive. The answer is that our script was smart, but not smart enough.
The problem this time turns out to be caused by the fact that we are now specifying a root directory ex. When the batch file removes the trailing backslash it generates [x:] which for a root directory only is not the same as with the backslash. The former specifies the default working directory while the latter is the root directory. Most of the time our users open a dedicated console for running this tool and never do any other work there.
But occasionally someone switches to the subst ed drive and goes to a subdirectory to do some other work. We fix it by adding a special case to not remove the trailing backslash for the special case of a root directory explicitly specified. This example was not intended to teach you what to do, but to give a reasonable example of how problems can creep in.
Before continuing, take a few moments and try to pick out the outer and the embedded quoted strings. You may be surprised to learn that all of these are interpreted exactly the same way by the command line parser— as a single argument: [Argument With Spaces]. But how can all of these possibly generate the same argument? One of the quotes is not even closed! The command line parser rules must be either inconsistent, incomprehensible, or just plain stupid. That way, a single percent sign will be used as literal within the command line, instead of being further interpreted.
However, the quotes themselves will be passed to the command too, unlike the double percent sign. Even linefeeds can be escaped this way, as is shown in the Useless Tips page. If you intend to "nest" commands with escaped characters, you may need to escape the escape character itself too.
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