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/Support/PrettyStackTrace.h"
  19 #include "llvm/Support/ToolOutputFile.h"
  20 #include "llvm/System/Signals.h"
  21 using namespace llvm;
  22
  23 static cl::opt<bool>
  24 Quiet("quiet", cl::desc("Don't print unnecessary status information"),
  25       cl::init(false));
  26
  27 static cl::opt<std::string>
  28 InputFilename("input-file", cl::desc("Input file (defaults to stdin)"),
  29               cl::init("-"), cl::value_desc("filename"));
  30
  31 static cl::opt<std::string>
  32 OutputFilename(cl::Positional, cl::desc("<output-file>"), cl::Required);
  33
  34 int main(int argc, char **argv) {
  35   sys::PrintStackTraceOnErrorSignal();
  36   PrettyStackTraceProgram X(argc, argv);
  37   cl::ParseCommandLineOptions(argc, argv);
  38
  39   if (OutputFilename == "-") {
  40     errs() << argv[0] << ": error: Can't update standard output\n";
  41     return 1;
  42   }
  43
  44   // Get the input data.
  45   std::string ErrorStr;
  46   MemoryBuffer *In =
  47     MemoryBuffer::getFileOrSTDIN(InputFilename.c_str(), &ErrorStr);
  48   if (In == 0) {
  49     errs() << argv[0] << ": error: Unable to get input '"
  50            << InputFilename << "': " << ErrorStr << '\n';
  51     return 1;
  52   }
  53
  54   // Get the output data.
  55   MemoryBuffer *Out = MemoryBuffer::getFile(OutputFilename.c_str(), &ErrorStr);
  56
  57   // If the output exists and the contents match, we are done.
  58   if (Out && In->getBufferSize() == Out->getBufferSize() &&
  59       memcmp(In->getBufferStart(), Out->getBufferStart(),
  60              Out->getBufferSize()) == 0) {
  61     if (!Quiet)
  62       errs() << argv[0] << ": Not updating '" << OutputFilename
  63              << "', contents match input.\n";
  64     return 0;
  65   }
  66
  67   delete Out;
  68
  69   // Otherwise, overwrite the output.
  70   if (!Quiet)
  71     errs() << argv[0] << ": Updating '" << OutputFilename
  72            << "', contents changed.\n";
  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 }