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How to add apostrophe as allowed character to existing regular expression?

I have the following regular expression for one of my name fields in C# web app:
^[A-Za-zÀ-ſ0-9.,#&-/'_!#;]?[a-zA-ZÀ-ſ0-9 '#&-/.,_:!#;]*[A-Za-zÀ-ſ0-9.,#-/_!#;]$
How can I properly modify it to add apostrophe/single quote character (') as an allowed character to it?

' is used for declaring a char, so put a backslash in front of the ' to escape it, like this \'.

It turned out that the RegEx has been fine, and it was the way the data has been input into database that caused the problem. Insert statements should have the apostrophes escaped. Even though the apostrophes were getting displayed correctly, they had been failing the RegEx check due to lack of escaping apostrophes. Thanks for your advice and sorry in case of any disapointment!

Regex not matching when input string contains an ampersand

I am trying to come up with a regex that starts with a letter followed by only letters, spaces, commas, dots, ampersands, apostrophes and hyphens.
However, the ampersand character is giving me headaches. Whenever it appears in the input string, the regex no longer matches.
I am using the regex in an ASP.net project using C# in the 'Format' property of a TextInput (a custom control created in the project). In it, I am using Regex.IsMatch(Text, Format) to match it.
For example, using this regex:
^[a-zA-Z][a-zA-Z&.,'\- ]*$
The results are:
John' william-david Pass
John, william'david allen--tony-'' Pass
John, william&david Fail
Whenever I put a & in the input string the regex no longer matches, but without it everything works fine.
How can I fix my issue? Why would the ampersand be causing a problem?
Notes:
I've tried to escape the ampersand with ^[a-zA-Z][a-zA-Z\&.,'\- ]*$ but it has the same issue
I've tried to put the ampersand at the beginning or end o ^[a-zA-Z][&a-zA-Z.,'\- ]*$ or ^[a-zA-Z][a-zA-Z.,'\-\& ]*$ but it also doesn't work

Your problem is somewhere else. The following expression evaluates to true:
Regex.IsMatch(#"John, william&david", #"^[a-zA-Z][a-zA-Z&.,'\- ]*$")
See https://dotnetfiddle.net/WDvQNP

You mentioned in the comments that your problem pertains to C#, so I'll answer your question in that context. If ampersand (&) is truly giving you issues in your character class, you should specify it in an alternate manner.
Luckily, C# supports hex escape sequences which means that you can specifying & as \x26.
For example, instead of:
^[a-zA-Z][a-zA-Z&.,'\- ]*$
use
^[a-zA-Z][a-zA-Z\x26.,'\- ]*$
If that doesn't fix your issue, then your issue is not the &, it's something else.

Replacing a specific character with string.replace()

I'd like to replace all occurences of / to \ . i used this snippet:
_url = _url.Replace("/",#"\");
but it replaces / to \\.
Why this happens? How can i modify the snippet to get a good result

Your string most likely already contains a single backslash!
I suspect your string already actually only contains a single backslash,
but you're looking at it in the debugger which is escaping it for you into
a form which would be valid as a regular string literal in C#.
quoted Jon Skeet from: Replace "\\" with "\" in a string in C#

I'm going to guess that you attempted to verify correct operation in the debugger. Visual Studio's debugger tips escape backslash characters, so if you see \\ in the tooltip then the string actually contains only 1 backslash. Click the magnifying glass icon at the end of the tooltip in the debugger to bring up a dialog containing the unescaped text.
Edit: This applies to the watch windows as well, including the part about the magnifying glass at the end.

Path/File name backslash in C#

I'm converting from VB to C#, and in C# I seem not to be able to simply write a path string to the application settings..
D:\Something becomes D:\\Something
I tried also #"D:\Something", but that also doesn't work.
So what is the correct way? Say I want to have two settings; path and filename. How shall I format them, for the purpose of Path.Combine to make this a valid file-path/name for a database, or in other words, to have single backslashes?

Your code is working correctly - when you read a string with doubled slashes back, they becomes single slashes again. This is called escaping. It is designed to let you enter special characters as sequences starting in \. Single slash becomes special in this scheme, so you need to escape it with a slash as well.

C# string - creating an unescaped backslash

I am using .NET (C#) code to write to a database that interfaces with a Perl application. When a single quote appears in a string, I need to "escape" it. IOW, the name O'Bannon should convert to O\'Bannon for the database UPDATE. However, all efforts at string manipulation (e.g. .Replace) generate an escape character for the backslash and I end up with O\\'Bannon.
I know it is actually generating the second backslash, because I can read the resulting database field's value (i.e. it is not just the IDE debug value for the string).
How can I get just the single backslash in the output string?
R

Well I did
"O'Bannon".Replace("'","\\'")
and result is
"O\'Bannon"
Is this what you want?

You can use "\\", which is the escape char followed by a backslash.
See the list of Escape Sequences here: http://msdn.microsoft.com/en-us/library/h21280bw.aspx

even better assign a var to the replace so that you can check it as well if needed
var RepName = "O'Bannon";
var Repstr = RepName.Replace("'","\\'");

You can also use a verbatim string
s = s.Replace("'", #"\'");