Many command interpreters and parsers provide their own sanitization and validation methods.

When available, their use is preferred over custom sanitization techniques because custom-developed sanitization can often neglect special cases or hidden complexities in the parser.

Furthermore, the textual representation of a path name may yield little or no information regarding the directory or file to which it refers.

validating input in perl-74

Many programs accept untrusted data originating from arbitrary users, network connections, and other untrusted sources and then pass the (modified or unmodified) data across a trust boundary to a different trusted domain.

Frequently the data is in the form of a string with some internal syntactic structure, which the subsystem must parse.

Another problem with custom sanitization code is that it may not be adequately maintained when new capabilities are added to the command interpreter or parser software.

This noncompliant code example demonstrates an XSS exploit.

For example, the final target of a symbolic link called file names makes it easier to validate a path name.

More than one path name can refer to a single directory or file.For example, some of the fields may only accept numbers while others may only accept dates, some fields may only accept a certain range of entries, some fields may be required, and some combinations of fields may not permitted.All of these examples must be handled by only two types of checks: the first is to validate each element user's input as the data is entered; the second is to perform the validation when the form is submitted. Absolute or relative path names may contain file links such as symbolic (soft) links, hard links, shortcuts, shadows, aliases, and junctions.These file links must be fully resolved before any file validation operations are performed.Java Script can validate input before it is sent to the server.