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In computer science, an illegal character is a character that is not allowed by a certain programming language, protocol, or program. [1] To avoid illegal characters, some languages may use an escape character which is a backslash followed by another character.
UNC names (any path starting with \\?\) do not support slashes. [4] The following examples show MS-DOS/Windows-style paths, with backslashes used to match the most common syntax: A:\Temp\File.txt This path points to a file with the name File.txt, located in the directory Temp, which in turn is located in the root directory of the drive A:.
A similar phenomenon occurs for DOS/Windows paths, where the backslash is used as a path separator, requiring a doubled backslash \\ – this can then be re-escaped for a regular expression inside an escaped string, requiring \\\\ to match a single backslash.
The string "localhost" will attempt to access the file as UNC path \\localhost\c:\path\to\the file.txt, which will not work since the colon is not allowed in a share name. The dot "." The dot "." results in the string being passed as \\.\c:\path\to\the file.txt , which will work for local files, but not shares on the local system.
Raw strings were originally included specifically for regular expressions. Due to limitations of the tokenizer, raw strings may not have a trailing backslash. [13] Creating a raw string holding a Windows path ending with a backslash requires some variety of workaround (commonly, using forward slashes instead of backslashes, since Windows ...
For example, in Python, raw strings are preceded by an r or R – compare 'C:\\Windows' with r'C:\Windows' (though, a Python raw string cannot end in an odd number of backslashes). Python 2 also distinguishes two types of strings: 8-bit ASCII ("bytes") strings (the default), explicitly indicated with a b or B prefix, and Unicode strings ...
The Microsoft Windows family of operating systems inherited the MS-DOS behavior and so still support either character – but individual Windows programs and sub-systems may, wrongly, only accept the backslash as a path delimiter, or may misinterpret a forward slash if it is used as such.
Without a preceding escape character, an * will expand to the names of all files in the working directory that do not start with a period if and only if there are such files, otherwise * remains unexpanded. So to refer to a file literally called "*", the shell must be told not to interpret it in this way, by preceding it with a backslash (\).