utils/FileUpdate/FileUpdate.cpp

   1 //===- FileUpdate.cpp - Conditionally update a file -----------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // FileUpdate is a utility for conditionally updating a file from its input
  11 // based on whether the input differs from the output. It is used to avoid
  12 // unnecessary modifications in a build system.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #include "llvm/Support/CommandLine.h"
  17 #include "llvm/Support/MemoryBuffer.h"
  18 #include "llvm/ADT/OwningPtr.h"
  19 #include "llvm/Support/PrettyStackTrace.h"
  20 #include "llvm/Support/ToolOutputFile.h"
  21 #include "llvm/Support/Signals.h"
  22 #include "llvm/Support/system_error.h"
  23 using namespace llvm;
  24
  25 static cl::opt<bool>
  26 Quiet("quiet", cl::desc("Don't print unnecessary status information"),
  27       cl::init(false));
  28
  29 static cl::opt<std::string>
  30 InputFilename("input-file", cl::desc("Input file (defaults to stdin)"),
  31               cl::init("-"), cl::value_desc("filename"));
  32
  33 static cl::opt<std::string>
  34 OutputFilename(cl::Positional, cl::desc("<output-file>"), cl::Required);
  35
  36 int main(int argc, char **argv) {
  37   sys::PrintStackTraceOnErrorSignal();
  38   PrettyStackTraceProgram X(argc, argv);
  39   cl::ParseCommandLineOptions(argc, argv);
  40
  41   if (OutputFilename == "-") {
  42     errs() << argv[0] << ": error: Can't update standard output\n";
  43     return 1;
  44   }
  45
  46   // Get the input data.
  47   OwningPtr<MemoryBuffer> In;
  48   if (error_code ec = MemoryBuffer::getFileOrSTDIN(InputFilename.c_str(), In)) {
  49     errs() << argv[0] << ": error: Unable to get input '"
  50            << InputFilename << "': " << ec.message() << '\n';
  51     return 1;
  52   }
  53
  54   // Get the output data.
  55   OwningPtr<MemoryBuffer> Out;
  56   MemoryBuffer::getFile(OutputFilename.c_str(), Out);
  57
  58   // If the output exists and the contents match, we are done.
  59   if (Out && In->getBufferSize() == Out->getBufferSize() &&
  60       memcmp(In->getBufferStart(), Out->getBufferStart(),
  61              Out->getBufferSize()) == 0) {
  62     if (!Quiet)
  63       errs() << argv[0] << ": Not updating '" << OutputFilename
  64              << "', contents match input.\n";
  65     return 0;
  66   }
  67
  68   // Otherwise, overwrite the output.
  69   if (!Quiet)
  70     errs() << argv[0] << ": Updating '" << OutputFilename
  71            << "', contents changed.\n";
  72   std::string ErrorStr;
  73   tool_output_file OutStream(OutputFilename.c_str(), ErrorStr,
  74                              raw_fd_ostream::F_Binary);
  75   if (!ErrorStr.empty()) {
  76     errs() << argv[0] << ": Unable to write output '"
  77            << OutputFilename << "': " << ErrorStr << '\n';
  78     return 1;
  79   }
  80
  81   OutStream.os().write(In->getBufferStart(), In->getBufferSize());
  82
  83   // Declare success.
  84   OutStream.keep();
  85
  86   return 0;
  87 }