Quickies for NSTask

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General

• Launching a task [permalink]
  Here are the basics to launch "ls -l -a -t" in the current directory, and then read the result into an NSString:

      NSTask *task;
      task = [[NSTask alloc] init];
      [task setLaunchPath: @"/bin/ls"];
  
      NSArray *arguments;
      arguments = [NSArray arrayWithObjects: @"-l", @"-a", @"-t", nil];
      [task setArguments: arguments];
  
      NSPipe *pipe;
      pipe = [NSPipe pipe];
      [task setStandardOutput: pipe];
  
      NSFileHandle *file;
      file = [pipe fileHandleForReading];
  
      [task launch];
  
      NSData *data;
      data = [file readDataToEndOfFile];
  
      NSString *string;
      string = [[NSString alloc] initWithData: data
                                 encoding: NSUTF8StringEncoding];
      NSLog (@"woop!  got\n%@", string);

  Of course, you can use different NSFileHandle methods for different styles of reading, and you can make a pipe for standard input so you can feed data to the task.

• Performing complex pipelines. [permalink]
  You can create multiple NSTasks and a bunch of NSPipes and hook them together, or you can use the "sh -c" trick to feed a shell a command, and let it parse it and set up all the IPC. This pipeline cats /usr/share/dict/words, finds all the words with 'ham' in them, reverses them, and shows you the last 5.

      NSTask *task;
      task = [[NSTask alloc] init];
      [task setLaunchPath: @"/bin/sh"];
  
      NSArray *arguments;
      arguments = [NSArray arrayWithObjects: @"-c",
                           @"cat /usr/share/dict/words | grep -i ham | rev | tail -5", nil];
      [task setArguments: arguments];
      // and then do all the other jazz for running an NSTask.

  One important note:, don't feed in arbitrary user data using this trick, since they could sneak in extra commands you probably don't want to execute.

• Stripping a string of all HTML tags via a perl script and NSTask [permalink]
  Here is a little perl script called stripper.pl which removes everything that looks like an HTML / SGML / XML tag:

  #!/usr/bin/perl
  
  while (<>) {
      $_ =~ s/<[^>]*>//gs;
      print $_;
  }
  

  Be sure to chmod +x the script. Add it to your project, add a new "Copy Files" phase, and have it stick this script into the Executables directory.

  This method will take a string and feed it through the perl script:

  - (NSString *) stringStrippedOfTags: (NSString *) string
  {
      NSBundle *bundle = [NSBundle mainBundle];
      NSString *stripperPath;
      stripperPath = [bundle pathForAuxiliaryExecutable: @"stripper.pl"];
  
      NSTask *task = [[NSTask alloc] init];
      [task setLaunchPath: stripperPath];
  
      NSPipe *readPipe = [NSPipe pipe];
      NSFileHandle *readHandle = [readPipe fileHandleForReading];
  
      NSPipe *writePipe = [NSPipe pipe];
      NSFileHandle *writeHandle = [writePipe fileHandleForWriting];
  
      [task setStandardInput: writePipe];
      [task setStandardOutput: readPipe];
  
      [task launch];
  
      [writeHandle writeData: [string dataUsingEncoding: NSASCIIStringEncoding]];
      [writeHandle closeFile];
  
      NSMutableData *data = [[NSMutableData alloc] init];
      NSData *readData;
  
      while ((readData = [readHandle availableData])
             && [readData length]) {
          [data appendData: readData];
      }
  
      NSString *strippedString;
      strippedString = [[NSString alloc]
                           initWithData: data
                           encoding: NSASCIIStringEncoding];
  
      [task release];
      [data release];
      [strippedString autorelease];
  
      return (strippedString);
  
  } // stringStrippedOfTags

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