Procedura: combinare query LINQ con espressioni regolari
Aggiornamento: novembre 2007
In questo esempio viene illustrato come utilizzare la classe Regex per creare un'espressione regolare per una corrispondenza più complessa nelle stringhe di testo. La query LINQ consente facilmente di filtrare esattamente in base ai file in cui si desidera eseguire la ricerca con l'espressione regolare e di elaborare i risultati.
Esempio
Class LinqRegExVB
Shared Sub Main()
' Root folder to query, along with all subfolders.
' Modify this path as necessary.
Dim startFolder As String = "C:\program files\Microsoft Visual Studio 9.0\"
' Take a snapshot of the file system.
Dim fileList As IEnumerable(Of System.IO.FileInfo) = GetFiles(startFolder)
' Create a regular expression to find all things "Visual".
Dim searchTerm As System.Text.RegularExpressions.Regex = _
New System.Text.RegularExpressions.Regex("Visual (Basic|C#|C\+\+|J#|SourceSafe|Studio)")
' Search the contents of each .htm file.
' Remove the where clause to find even more matches!
' This query produces a list of files where a match
' was found, and a list of the matches in that file.
' Note: Explicit typing of "Match" in select clause.
' This is required because MatchCollection is not a
' generic IEnumerable collection.
Dim queryMatchingFiles = From afile In fileList _
Where afile.Extension = ".htm" _
Let fileText = System.IO.File.ReadAllText(afile.FullName) _
Let matches = searchTerm.Matches(fileText) _
Where (searchTerm.Matches(fileText).Count > 0) _
Select Name = afile.FullName, _
Matches = From match As System.Text.RegularExpressions.Match In matches _
Select match.Value
' Execute the query.
Console.WriteLine("The term " & searchTerm.ToString() & " was found in:")
For Each fileMatches In queryMatchingFiles
' Trim the path a bit, then write
' the file name in which a match was found.
Dim s = fileMatches.Name.Substring(startFolder.Length - 1)
Console.WriteLine(s)
' For this file, write out all the matching strings
For Each match In fileMatches.Matches
Console.WriteLine(" " + match)
Next
Next
' Keep the console window open in debug mode
Console.WriteLine("Press any key to exit")
Console.ReadKey()
End Sub
' Function to retrieve a list of files. Note that this is a copy
' of the file information.
Shared Function GetFiles(ByVal root As String) As IEnumerable(Of System.IO.FileInfo)
Return From file In My.Computer.FileSystem.GetFiles _
(root, FileIO.SearchOption.SearchAllSubDirectories, "*.*") _
Select New System.IO.FileInfo(file)
End Function
End Class
class QueryWithRegEx
{
public static void Main()
{
// Modify this path as necessary.
string startFolder = @"c:\program files\Microsoft Visual Studio 9.0\";
// Take a snapshot of the file system.
IEnumerable<System.IO.FileInfo> fileList = GetFiles(startFolder);
// Create the regular expression to find all things "Visual".
System.Text.RegularExpressions.Regex searchTerm =
new System.Text.RegularExpressions.Regex(@"Visual (Basic|C#|C\+\+|J#|SourceSafe|Studio)");
// Search the contents of each .htm file.
// Remove the where clause to find even more matches!
// This query produces a list of files where a match
// was found, and a list of the matches in that file.
// Note: Explicit typing of "Match" in select clause.
// This is required because MatchCollection is not a
// generic IEnumerable collection.
var queryMatchingFiles =
from file in fileList
where file.Extension == ".htm"
let fileText = System.IO.File.ReadAllText(file.FullName)
let matches = searchTerm.Matches(fileText)
where searchTerm.Matches(fileText).Count > 0
select new
{
name = file.FullName,
matches = from System.Text.RegularExpressions.Match match in matches
select match.Value
};
// Execute the query.
Console.WriteLine("The term \"{0}\" was found in:", searchTerm.ToString());
foreach (var v in queryMatchingFiles)
{
// Trim the path a bit, then write
// the file name in which a match was found.
string s = v.name.Substring(startFolder.Length - 1);
Console.WriteLine(s);
// For this file, write out all the matching strings
foreach (var v2 in v.matches)
{
Console.WriteLine(" " + v2);
}
}
// Keep the console window open in debug mode
Console.WriteLine("Press any key to exit");
Console.ReadKey();
}
// This method assumes that the application has discovery
// permissions for all folders under the specified path.
static IEnumerable<System.IO.FileInfo> GetFiles(string path)
{
if (!System.IO.Directory.Exists(path))
throw new System.IO.DirectoryNotFoundException();
string[] fileNames = null;
List<System.IO.FileInfo> files = new List<System.IO.FileInfo>();
fileNames = System.IO.Directory.GetFiles(path, "*.*", System.IO.SearchOption.AllDirectories);
foreach (string name in fileNames)
{
files.Add(new System.IO.FileInfo(name));
}
return files;
}
}
È inoltre possibile eseguire una query sull'oggetto MatchCollection restituito da una ricerca RegEx. In questo esempio nei risultati viene generato solo il valore di ogni corrispondenza. Tuttavia, è anche possibile utilizzare LINQ per eseguire tutti i tipi di filtro, ordinamento e raggruppamento su tale insieme. Poiché MatchCollection è un insieme IEnumerable non generico, è necessario dichiarare in modo esplicito il tipo della variabile di intervallo nella query.
Compilazione del codice
Creare un progetto di Visual Studio destinato a .NET Framework versione 3.5. Per impostazione predefinita, il progetto contiene un riferimento a System.Core.dll e una direttiva using (C#) o un'istruzione Imports (Visual Basic) per lo spazio dei nomi System.Linq. Nei progetti C# aggiungere una direttiva using per lo spazio dei nomi System.IO.
Copiare questo codice nel progetto.
Premere F5 per compilare ed eseguire il programma.
Premere un tasto per chiudere la finestra della console.
Vedere anche
Attività
Procedura: generare codice XML da file CSV