本文实例讲述了C#从文件或标准输入设备读取指定行的方法。分享给大家供大家参考。具体如下：

using System;using System.IO;using System.Runtime.InteropServices;using System.Text.RegularExpressions;using System.Collections.Generic;namespace RobvanderWoude{ class ReadLine { static int Main( string[] args ) { #region Command Line Parsing string filename = string.Empty; int linestart = 1; int lineend = 2; bool concat = false; bool addspaces = false; string concatchar = string.Empty; bool skipempty = false; bool trimlines = false; bool numlines = false; bool redirected; bool set_c = false; bool set_l = false; bool set_s = false; bool set_t = false; bool set_input = false; if ( ConsoleEx.InputRedirected ) { set_input = true; redirected = true; } else { if ( args.Length == 0 ) { return WriteError( ); } redirected = false; } foreach ( string arg in args ) { if ( arg[0] == '/' ) { try { switch ( arg.ToUpper( )[1] ) { case '?': return WriteError( ); case 'C': if ( arg.ToUpper( ) != "/C" && arg.ToUpper( ) != "/CS" ) { return WriteError( "Invalid command line switch " + arg ); } concat = true; if ( arg.ToUpper( ) == "/CS" ) { addspaces = true; } if ( set_c ) { return WriteError( "Duplicate command line argument /C*" ); } set_c = true; break; case 'L': if(arg.ToUpper( ).StartsWith( "/L:" ) && arg.Length > 3) { if ( arg[2] == ':' ) { string linessel = arg.Substring( 3 ); string pattern = @"^(\-?\d+)$"; Match match = Regex.Match( linessel, pattern ); if ( match.Success ) { linestart = Convert.ToInt32( match.Groups[1].Value ); lineend = linestart + 1; } else { pattern = @"^(\-?\d+)\.\.(\-?\d+)$"; match = Regex.Match( linessel, pattern ); if ( match.Success ) { linestart = Convert.ToInt32( match.Groups[1].Value ); lineend = Convert.ToInt32( match.Groups[2].Value ) + 1; } else { pattern = @"^(\-?\d+),(\-?\d+)$"; match = Regex.Match( linessel, pattern ); if ( match.Success ) { // numlines is true if the second number //specifies the number of lines instead of a line number numlines = true; linestart = Convert.ToInt32( match.Groups[1].Value ); lineend = Convert.ToInt32( match.Groups[2].Value ); if ( lineend < 1 ) { return WriteError( "Invalid number of lines (" + lineend.ToString( ) + "), must be 1 or higher" ); } } } } } else { return WriteError( "Invalid command line switch " + arg ); } } else { return WriteError( "Invalid command line switch " + arg ); } if ( set_l ) { return WriteError( "Duplicate command line argument /L" ); } set_l = true; break; case 'S': if ( arg.ToUpper( ) != "/SE" ) { return WriteError( "Invalid command line switch " + arg ); } skipempty = true; if ( set_s ) { return WriteError( "Duplicate command line argument /SE" ); } set_s = true; break; case 'T': if ( arg.ToUpper( ) != "/T" ) { return WriteError( "Invalid command line switch " + arg ); } trimlines = true; if ( set_t ) { return WriteError( "Duplicate command line argument /T" ); } set_t = true; break; default: return WriteError( "Invalid command line switch " + arg ); } } catch { return WriteError( "Invalid command line switch " + arg ); } } else { if ( set_input ) { return WriteError( "Multiple inputs specified (file + redirection or multiple files)" ); } if ( redirected ) { return WriteError( "Do not specify a file name when using redirected input" ); } else { filename = arg; } } } #endregion try { int count = 0; bool output = false; string[] lines; List<string> alllines = new List<string>( ); if ( redirected ) { // Read standard input and store the lines in a list int peek = 0; do { alllines.Add( Console.In.ReadLine( ) ); } while ( peek != -1 ); // Convert the list to an array lines = alllines.ToArray( ); } else { // Read the file and store the lines in a list lines = File.ReadAllLines( filename ); } // Check if negative numbers were used, and if so, //calculate the resulting line numbers if ( linestart < 0 ) { linestart += lines.Length + 1; } if ( lineend < 0 ) { lineend += lines.Length + 1; } if ( numlines ) { lineend += linestart; } // Iterate through the array of lines and display //the ones matching the command line switches foreach ( string line in lines ) { string myline = line; if ( trimlines ) { myline = myline.Trim( ); } bool skip = skipempty && ( myline.Trim( ) == string.Empty ); if ( !skip ) { count += 1; if ( count >= linestart && count < lineend ) { if ( concat ) { Console.Write( "{0}{1}", concatchar, myline ); } else { Console.WriteLine( myline ); } if ( addspaces ) { concatchar = " "; } } } } } catch ( Exception e ) { return WriteError( e.Message ); } return 0; } #region Redirection Detection public static class ConsoleEx { public static bool OutputRedirected { get { return FileType.Char != GetFileType( GetStdHandle( StdHandle.Stdout ) ); } } public static bool InputRedirected { get { return FileType.Char != GetFileType( GetStdHandle( StdHandle.Stdin ) ); } } public static bool ErrorRedirected { get { return FileType.Char != GetFileType( GetStdHandle( StdHandle.Stderr ) ); } } // P/Invoke: private enum FileType { Unknown, Disk, Char, Pipe }; private enum StdHandle { Stdin = -10, Stdout = -11, Stderr = -12 }; [DllImport( "kernel32.dll" )] private static extern FileType GetFileType( IntPtr hdl ); [DllImport( "kernel32.dll" )] private static extern IntPtr GetStdHandle( StdHandle std ); } #endregion #region Error Handling public static int WriteError( Exception e = null ) { return WriteError( e == null ? null : e.Message ); } public static int WriteError( string errorMessage ) { if ( string.IsNullOrEmpty( errorMessage ) == false ) { Console.Error.WriteLine( ); Console.ForegroundColor = ConsoleColor.Red; Console.Error.Write( "ERROR: " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.WriteLine( errorMessage ); Console.ResetColor( ); } Console.Error.WriteLine( ); Console.Error.WriteLine( "ReadLine, Version 0.30 beta" ); Console.Error.WriteLine( "Return the specified line(s) from a file or Standard Input" ); Console.Error.WriteLine( ); Console.Error.Write( "Usage: " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.WriteLine( "READLINE filename [ options ]" ); Console.ResetColor( ); Console.Error.Write( " or: " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.WriteLine( "READLINE [ options ] < filename" ); Console.ResetColor( ); Console.Error.Write( " or: " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.WriteLine( "command | READLINE [ options ]" ); Console.ResetColor( ); Console.Error.WriteLine( ); Console.Error.Write( "Where: " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( "filename" ); Console.ResetColor( ); Console.Error.WriteLine( " is the optional file to be read" ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( " command" ); Console.ResetColor( ); Console.Error.WriteLine( " is the optional command whose output is to be read" ); Console.Error.WriteLine( ); Console.Error.Write( "Options: " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( "/C C" ); Console.ResetColor( ); Console.Error.WriteLine( "oncatenate lines" ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( " /CS C" ); Console.ResetColor( ); Console.Error.Write( "oncatenate lines with " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( "S" ); Console.ResetColor( ); Console.Error.WriteLine( "paces in between" ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( " /L:n" ); Console.ResetColor( ); Console.Error.Write( " read line " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.WriteLine( "n" ); Console.ResetColor( ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( " /L:n..m" ); Console.ResetColor( ); Console.Error.Write( " read lines " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( "n" ); Console.ResetColor( ); Console.Error.Write( " through " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.WriteLine( "m" ); Console.Error.Write( " /L:n,m" ); Console.ResetColor( ); Console.Error.Write( " read " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( "m" ); Console.ResetColor( ); Console.Error.Write( " lines starting at line " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.WriteLine( "n" ); Console.ResetColor( ); Console.Error.WriteLine( "(negative numbers start counting from the end backwards)" ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( " /SE S" ); Console.ResetColor( ); Console.Error.Write( "kip " ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( "E" ); Console.ResetColor( ); Console.Error.WriteLine( "mpty lines" ); Console.ForegroundColor = ConsoleColor.White; Console.Error.Write( " /T T" ); Console.ResetColor( ); Console.Error.WriteLine( "rim leading and trailing whitespace from lines" ); Console.Error.WriteLine( ); Console.Error.WriteLine( "Examples:" ); Console.Error.WriteLine( "READLINE file read the first non-empty line (default)" ); Console.Error.WriteLine( "READLINE file /L:2 /SE read the second non-empty line of file" ); Console.Error.WriteLine( "READLINE file /L:5..7 read lines 5..7 of file" ); Console.Error.WriteLine( "READLINE file /L:-1 read the last line of file" ); Console.Error.WriteLine( "READLINE file /L:-2..-1 read the last 2 lines of file" ); Console.Error.WriteLine( "READLINE file /L:-2,2 read the last 2 lines of file" ); Console.Error.WriteLine( ); Console.Error.Write( "Check for redirection by Hans Passant on " ); Console.ForegroundColor = ConsoleColor.DarkGray; Console.Error.WriteLine( "StackOverflow.com" ); Console.Error.WriteLine( "/questions/3453220/how-to-detect-if-console-in-stdin-has-been-redirected" ); Console.ResetColor( ); Console.Error.WriteLine( ); Console.Error.WriteLine( "Written by Rob van der Woude" ); return 1; } #endregion }}

希望本文所述对大家的C#程序设计有所帮助。