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+// file : butl/pager -*- C++ -*-
+// copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
+// license : MIT; see accompanying LICENSE file
+
+#ifndef BUTL_PAGER
+#define BUTL_PAGER
+
+#include <string>
+#include <vector>
+#include <iostream>
+
+#include <butl/process>
+#include <butl/fdstream>
+
+namespace butl
+{
+ // Try to run the output through a pager program, such as more or less (no
+ // pun intended, less is used by default). If the default pager program is
+ // used, then the output is indented so that 80-character long lines will
+ // appear centered in the terminal. If the default pager program fails to
+ // start, then the output is sent directly to STDOUT.
+ //
+ // If the pager program is specified and is empty, then no pager is used
+ // and the output is sent directly to STDOUT.
+ //
+ // Throw std::system_error if there are problems with the pager program.
+ //
+ // Typical usage:
+ //
+ // try
+ // {
+ // pager p ("help for foo");
+ // ostream& os (p.stream ());
+ //
+ // os << "Foo is such and so ...";
+ //
+ // if (!p.wait ())
+ // ... // Pager program returned non-zero status.
+ // }
+ // catch (const std::system_error& e)
+ // {
+ // cerr << "pager error: " << e.what () << endl;
+ // }
+ //
+ class pager: protected std::streambuf
+ {
+ public:
+ ~pager () {wait ();}
+
+ // If verbose is true, then print (to STDERR) the pager command line.
+ //
+ pager (const std::string& name,
+ bool verbose = false,
+ const std::string* pager = nullptr,
+ const std::vector<std::string>* pager_options = nullptr);
+
+ std::ostream&
+ stream () {return os_.is_open () ? os_ : std::cout;}
+
+ bool
+ wait ();
+
+ // The streambuf output interface that implements indentation. You can
+ // override it to implement custom output pre-processing.
+ //
+ protected:
+ using int_type = std::streambuf::int_type;
+ using traits_type = std::streambuf::traits_type;
+
+ virtual int_type
+ overflow (int_type);
+
+ virtual int
+ sync ();
+
+ private:
+ process p_;
+ ofdstream os_;
+
+ std::string indent_;
+ int_type prev_ = '\n'; // Previous character.
+ std::streambuf* buf_ = nullptr;
+ };
+};
+
+#endif // BUTL_PAGER