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Regex - File Path - Windows

^(?:[a-zA-Z]:\\$)|^(?:[a-zA-Z]\:|\\)(\\(?!\.)(?!\s[a-zA-Z_0-9-\.])[a-zA-Z_\-\s0-9\.\$]+)+$

or 

^(\w:\\$)|^(?:[\w]\:|\\)(\\(?!\.)(?!\s[a-zA-Z_0-9-])[a-zA-Z_\-\s0-9\.\$]+)+$

NOTE: This is made up of:

^(?:[a-zA-Z]:\\$): Caters for C:\.
^(?:[a-zA-Z]\:|\\)(\\(?!\.)(?!\s[a-zA-Z_0-9-\.])[a-zA-Z_\-\s0-9\.\$]+)+$: Cater for UNC and standard files with a directory name.

^(\w:\\$): Caters for C:\.
^(?:[\w]\:|\\)(\\(?!\.)(?!\s[a-zA-Z_0-9-])[A-Za-z_\-\s0-9\.\$]+)+$: Cater for UNC and standard files with a directory name.

NOTE: This regex supports the following as valid.

c:\
c:\folder\myfile.txt
c:\folder\myfileWithoutExtension
c:\my folder\abc abc.docx
c:\my-folder\another_folder\abc.v2.docx
C:\pictures\holiday  
C:\pictures\holiday\ 
\\192.168.0.1\folder\file.pdf
\\192.168.0.1\my folder\folder.2\file.gif
\\10.30.28.52\CDSDataCenter\Servers\Continuous\CDS20$
\\server\filename
\\server\filename with space
\\test\test$\TEST.xls
\\server\share\folder\myfile.txt
\\server\share\myfile.txt
\\123.123.123.123\share\folder\myfile.txt

NOTE: The following are not valid:

file
file.xls
c:\my folder\another_folder\.docx
c:\my folder\\another_folder\abc.docx
c:\my folder\another_folder\ab*c.v2.docx
c:\my?folder\another_folder\abc.v2.docx
C:\ pictures\holiday
C:\ pictures\holiday\
C:\pictures \ holiday
C:\pictures \ holiday\
C:\pictures\ holiday \
\\192.168.0.1\folder\fi<le.pdf
\\192.168.0.1\folder\\file.pdf
\\192.168.0.1\my folder\folder.2\.gif
\\server\filename\{token}\file

To allow the top two entries to also be accepted as valid entries change the regex to include:

^([A-Za-z_\-\s0-9\.\$]+)$: Caters for plain filenames, such as file.txt or file.

^(\w:\\$)|^([A-Za-z_\-\s0-9\.\$]+)$|^(?:[\w]\:|\\)(\\(?!\.)(?!\s[a-z_0-9-])[A-Za-z_\-\s0-9\.\$]+)+$

^(?:[\w]\:|\\)(\\(?!\.+)[A-Za-z_\-\s0-9\.\$]+)+$

Works….

(?:[\w]\:

(?:[\w]\:

([a-z_\-\s\0-9\.\\]+)+([a-z_\-\s\0-9\.]+)(\\)([a-z_\-\s\0-9]+)$

^(?:[\w]\:|\\)(\\[a-z_\-\s0-9\.]+)+\.(txt|gif|pdf|doc|docx|xls|xlsx)$

^(?:[\w]\:|\\)(\\[a-z_\-\s\0-9\.]+)+(?:\\)([a-z_\-\s\0-9]+){1}$

(?:(?:[a-z]:|\\\\[a-z0-9_.$\●-]+\\[a-z0-9_.$\●-]+)\\|  # Drive
   \\?[^\\/:*?"<>|\r\n]+\\?)                           # Relative path
(?:[^\\/:*?"<>|\r\n]+\\)*                              # Folder
[^\\/:*?"<>|\r\n]*                                     # File


^(?:[\w]\:\\|\\\\)([a-z0-9_.$\s-]+\\[a-z0-9_.$\.-]+\\|\\?[^\\/:*?"<>|\r\n]+\\?)(?:[^\\/:*?"<>|\r\n]+\\)*[^\\/:*?"<>|\r\n]*$

Windows

(\\\\([a-z|A-Z|0-9|-|_|\s]{2,15}){1}(\.[a-z|A-Z|0-9|-|_|\s]{1,64}){0,3}){1}(\\[^\\|\/|\:|\*|\?|"|\<|\>|\|]{1,64}){1,}(\\){0,}

NOTE: Disallows a few characters: \/:*?"<>|.

^((?:[a-z]:\\$|(?:[a-z]:|\\\\[a-z]+\\(?!\.)[^\r\n$<>]+\$?)))((\\|(\\(?!\.)[^\r\n<>\\]+)*)(?<!\\)$)

^[a-zA-Z]:\\(((?![<>:"/\\|?*]).)+((?<![ .])\\)?)*$

NOTE: It makes the path conform to the NTFS standard (see the MSDN spec).

^[a-zA-Z]:\\ matches single drive letter, with colon and backslash

(?![<>:"/\\|?*]) is a negative lookahead to ensure the next character is not invalid

((?![<>:"/\\|?*]).)+ wraps that lookahead, followed by the next character, any number of times

(?<![ .])\\ is a negative lookbehind to ensure the file/directory doesn't end with a space or period. Please note: Lookbehinds are not fully implemented everywhere just yet.

All of that is is repeated 0 to many times, with the last backslash optional.

For many use cases it may be best to restrict the path length to 256 characters.

To do so, replace *with {0,256}.

References

https://www.regexpal.com/97685

Wiki

Table of Contents

Regex - File Path - Windows

Windows

References