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What does this part mean: <i>(of all countries)</i>? &nbsp;What is your character encoding?
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What does this part mean: (of all countries)?  What is your character encoding?

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Do you have any text file or some file in any format which contains the list of all countries which is having mixture of number, lowercase,uppercase and so on in it?<br />
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If you can give one example then we could generate the patter for it.
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Do you have any text file or some file in any format which contains the list of all countries which is having mixture of number, lowercase,uppercase and so on in it?

If you can give one example then we could generate the patter for it.

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regular expression<br />
only want numbers and lowercase &amp;&nbsp;uppercase letters (of all countries)
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regular expression
only want numbers and lowercase & uppercase letters (of all countries)

only want numbers and lowercase &amp; uppercase letters (of all countries)

A regular expression ("regex") is a sequence of characters that define a search pattern, mainly for use in pattern matching with strings, or string matching, i.e. "find and replace"-like operations. Regular expression processors are found in several search engines, search and replace dialogs of several word processors and text editors, and in the command lines of text processing utilities, such as sed and AWK. Many programming languages provide regular expression capabilities, some built-in, for example Perl, JavaScript, Ruby, AWK, and Tcl, and others via a standard library, for example .NET languages, Java, Python and C++ (since C++11). Most other languages offer regular expressions via a library.

Regular Expressions

PHP is a widely-used server-side scripting language especially suited for web development, powering tens of millions of sites from Facebook to personal WordPress blogs. PHP is often paired with the MySQL relational database, but includes support for most other mainstream databases. By utilizing different Server APIs, PHP can work on many different web servers as a server-side scripting language.

only want numbers and lowercase &amp; uppercase letters (of all countries)

only want numbers and lowercase & uppercase letters (of all countries)