C#

//open a file
FileStream fs = new FileStream(fileName);
StreamReader reader = new StreamReader(fs);

//loop over the lines
String line = String.Empty
while( (line = reader.ReadLine()) != null ){
   
  //match a simple substring  

  if(line.indexOf("something") > 0){
    Console.WriteLine( line );  
  }
 
  //or match a regular expression
 
  Regexp epression = new Regex("~m/something/")
  if(expression.IsMatch(line)){
    Console.WrileLine(line);
  }

}

reader.close();