1 //===- FileUpdate.cpp - Conditionally update a file -----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Support/CommandLine.h"
17 #include "llvm/Support/FileSystem.h"
18 #include "llvm/Support/MemoryBuffer.h"
19 #include "llvm/Support/PrettyStackTrace.h"
20 #include "llvm/Support/Signals.h"
21 #include "llvm/Support/ToolOutputFile.h"
22 #include <system_error>
24 using std::error_code;
27 Quiet("quiet", cl::desc("Don't print unnecessary status information"),
30 static cl::opt<std::string>
31 InputFilename("input-file", cl::desc("Input file (defaults to stdin)"),
32 cl::init("-"), cl::value_desc("filename"));
34 static cl::opt<std::string>
35 OutputFilename(cl::Positional, cl::desc("<output-file>"), cl::Required);
37 int main(int argc, char **argv) {
38 sys::PrintStackTraceOnErrorSignal();
39 PrettyStackTraceProgram X(argc, argv);
40 cl::ParseCommandLineOptions(argc, argv);
42 if (OutputFilename == "-") {
43 errs() << argv[0] << ": error: Can't update standard output\n";
47 // Get the input data.
48 std::unique_ptr<MemoryBuffer> In;
49 if (error_code ec = MemoryBuffer::getFileOrSTDIN(InputFilename, In)) {
50 errs() << argv[0] << ": error: Unable to get input '"
51 << InputFilename << "': " << ec.message() << '\n';
55 // Get the output data.
56 std::unique_ptr<MemoryBuffer> Out;
57 MemoryBuffer::getFile(OutputFilename.c_str(), Out);
59 // If the output exists and the contents match, we are done.
60 if (Out && In->getBufferSize() == Out->getBufferSize() &&
61 memcmp(In->getBufferStart(), Out->getBufferStart(),
62 Out->getBufferSize()) == 0) {
64 errs() << argv[0] << ": Not updating '" << OutputFilename
65 << "', contents match input.\n";
69 // Otherwise, overwrite the output.
71 errs() << argv[0] << ": Updating '" << OutputFilename
72 << "', contents changed.\n";
74 tool_output_file OutStream(OutputFilename.c_str(), ErrorStr,
76 if (!ErrorStr.empty()) {
77 errs() << argv[0] << ": Unable to write output '"
78 << OutputFilename << "': " << ErrorStr << '\n';
82 OutStream.os().write(In->getBufferStart(), In->getBufferSize());