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# Copyright (C) 2009-2012 Chris Ball <cjb@laptop.org>
# W. Trevor King <wking@tremily.us>
#
# This file is part of Bugs Everywhere.
#
# Bugs Everywhere is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 2 of the License, or (at your option) any
# later version.
#
# Bugs Everywhere is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
# more details.
#
# You should have received a copy of the GNU General Public License along with
# Bugs Everywhere. If not, see <http://www.gnu.org/licenses/>.
"""Automatic pager for terminal output (a la Git).
"""
import os as _os
import select as _select
import shlex as _shlex
import sys as _sys
# Inspired by Nathan Weizenbaum's
# http://nex-3.com/posts/73-git-style-automatic-paging-in-ruby
def run_pager(paginate='auto'):
"""Use the environment variable PAGER page future stdout output
paginate should be one of 'never', 'auto', or 'always'.
usage: just call this function and continue using sys.stdout like
you normally would.
Notes
-----
This function creates forks a child, which continues executing the
calling code. The parent calls :py:func:`os.execvpe` to morph
into `PAGER`. The child keeps the original stdin, and the child's
stdout becomes the parent's stdin. The parent keeps the original
stdout.
"""
if (paginate == 'never' or
_sys.platform == 'win32' or
not hasattr(_sys.stdout, 'isatty') or
not _sys.stdout.isatty()):
return
env = dict(_os.environ)
if paginate == 'auto':
if 'LESS' not in env:
env['LESS'] = '' # += doesn't work on undefined var
else:
env['LESS'] += ' ' # separate from existing variables
# don't page if the input is short enough
env['LESS'] += '-FRX'
pager = _os.environ.get('PAGER', 'less')
args = _shlex.split(pager)
pager = args[0]
if not pager: # handle PAGER=''
return
read_fd, write_fd = _os.pipe()
if _os.fork() == 0:
# child process, keep executing Python program
_os.close(read_fd)
_os.dup2(write_fd, 1)
_os.close(write_fd)
if hasattr(_sys.stderr, 'isatty') and _sys.stderr.isatty():
_os.dup2(1, 2)
return
# parent process, become pager
_os.close(write_fd)
_os.dup2(read_fd, 0)
_os.close(read_fd)
# Wait until we have input before we start the pager
_select.select([0], [], [])
_os.execvpe(pager, args, env)
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