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9bce311ea4
This function used to live as pipes.quote, where it was undocumented but used anyway. (An alias still exists for backward compatibility.) The tests have been moved as is, but the code of the function was changed to use a regex instead of a loop with string comparisons (at Ian Bicking’s suggestion). I’m terrible at regexes, so any feedback is welcome.
250 lines
8.8 KiB
Python
250 lines
8.8 KiB
Python
"""Conversion pipeline templates.
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The problem:
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------------
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Suppose you have some data that you want to convert to another format,
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such as from GIF image format to PPM image format. Maybe the
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conversion involves several steps (e.g. piping it through compress or
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uuencode). Some of the conversion steps may require that their input
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is a disk file, others may be able to read standard input; similar for
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their output. The input to the entire conversion may also be read
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from a disk file or from an open file, and similar for its output.
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The module lets you construct a pipeline template by sticking one or
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more conversion steps together. It will take care of creating and
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removing temporary files if they are necessary to hold intermediate
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data. You can then use the template to do conversions from many
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different sources to many different destinations. The temporary
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file names used are different each time the template is used.
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The templates are objects so you can create templates for many
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different conversion steps and store them in a dictionary, for
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instance.
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Directions:
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-----------
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To create a template:
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t = Template()
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To add a conversion step to a template:
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t.append(command, kind)
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where kind is a string of two characters: the first is '-' if the
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command reads its standard input or 'f' if it requires a file; the
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second likewise for the output. The command must be valid /bin/sh
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syntax. If input or output files are required, they are passed as
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$IN and $OUT; otherwise, it must be possible to use the command in
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a pipeline.
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To add a conversion step at the beginning:
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t.prepend(command, kind)
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To convert a file to another file using a template:
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sts = t.copy(infile, outfile)
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If infile or outfile are the empty string, standard input is read or
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standard output is written, respectively. The return value is the
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exit status of the conversion pipeline.
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To open a file for reading or writing through a conversion pipeline:
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fp = t.open(file, mode)
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where mode is 'r' to read the file, or 'w' to write it -- just like
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for the built-in function open() or for os.popen().
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To create a new template object initialized to a given one:
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t2 = t.clone()
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For an example, see the function test() at the end of the file.
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""" # '
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import re
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import os
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import tempfile
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# we import the quote function rather than the module for backward compat
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# (quote used to be an undocumented but used function in pipes)
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from shlex import quote
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__all__ = ["Template"]
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# Conversion step kinds
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FILEIN_FILEOUT = 'ff' # Must read & write real files
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STDIN_FILEOUT = '-f' # Must write a real file
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FILEIN_STDOUT = 'f-' # Must read a real file
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STDIN_STDOUT = '--' # Normal pipeline element
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SOURCE = '.-' # Must be first, writes stdout
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SINK = '-.' # Must be last, reads stdin
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stepkinds = [FILEIN_FILEOUT, STDIN_FILEOUT, FILEIN_STDOUT, STDIN_STDOUT, \
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SOURCE, SINK]
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class Template:
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"""Class representing a pipeline template."""
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def __init__(self):
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"""Template() returns a fresh pipeline template."""
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self.debugging = 0
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self.reset()
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def __repr__(self):
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"""t.__repr__() implements repr(t)."""
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return '<Template instance, steps=%r>' % (self.steps,)
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def reset(self):
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"""t.reset() restores a pipeline template to its initial state."""
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self.steps = []
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def clone(self):
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"""t.clone() returns a new pipeline template with identical
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initial state as the current one."""
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t = Template()
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t.steps = self.steps[:]
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t.debugging = self.debugging
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return t
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def debug(self, flag):
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"""t.debug(flag) turns debugging on or off."""
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self.debugging = flag
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def append(self, cmd, kind):
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"""t.append(cmd, kind) adds a new step at the end."""
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if type(cmd) is not type(''):
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raise TypeError('Template.append: cmd must be a string')
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if kind not in stepkinds:
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raise ValueError('Template.append: bad kind %r' % (kind,))
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if kind == SOURCE:
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raise ValueError('Template.append: SOURCE can only be prepended')
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if self.steps and self.steps[-1][1] == SINK:
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raise ValueError('Template.append: already ends with SINK')
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if kind[0] == 'f' and not re.search(r'\$IN\b', cmd):
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raise ValueError('Template.append: missing $IN in cmd')
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if kind[1] == 'f' and not re.search(r'\$OUT\b', cmd):
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raise ValueError('Template.append: missing $OUT in cmd')
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self.steps.append((cmd, kind))
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def prepend(self, cmd, kind):
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"""t.prepend(cmd, kind) adds a new step at the front."""
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if type(cmd) is not type(''):
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raise TypeError('Template.prepend: cmd must be a string')
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if kind not in stepkinds:
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raise ValueError('Template.prepend: bad kind %r' % (kind,))
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if kind == SINK:
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raise ValueError('Template.prepend: SINK can only be appended')
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if self.steps and self.steps[0][1] == SOURCE:
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raise ValueError('Template.prepend: already begins with SOURCE')
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if kind[0] == 'f' and not re.search(r'\$IN\b', cmd):
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raise ValueError('Template.prepend: missing $IN in cmd')
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if kind[1] == 'f' and not re.search(r'\$OUT\b', cmd):
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raise ValueError('Template.prepend: missing $OUT in cmd')
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self.steps.insert(0, (cmd, kind))
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def open(self, file, rw):
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"""t.open(file, rw) returns a pipe or file object open for
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reading or writing; the file is the other end of the pipeline."""
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if rw == 'r':
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return self.open_r(file)
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if rw == 'w':
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return self.open_w(file)
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raise ValueError('Template.open: rw must be \'r\' or \'w\', not %r'
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% (rw,))
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def open_r(self, file):
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"""t.open_r(file) and t.open_w(file) implement
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t.open(file, 'r') and t.open(file, 'w') respectively."""
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if not self.steps:
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return open(file, 'r')
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if self.steps[-1][1] == SINK:
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raise ValueError('Template.open_r: pipeline ends width SINK')
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cmd = self.makepipeline(file, '')
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return os.popen(cmd, 'r')
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def open_w(self, file):
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if not self.steps:
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return open(file, 'w')
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if self.steps[0][1] == SOURCE:
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raise ValueError('Template.open_w: pipeline begins with SOURCE')
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cmd = self.makepipeline('', file)
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return os.popen(cmd, 'w')
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def copy(self, infile, outfile):
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return os.system(self.makepipeline(infile, outfile))
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def makepipeline(self, infile, outfile):
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cmd = makepipeline(infile, self.steps, outfile)
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if self.debugging:
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print(cmd)
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cmd = 'set -x; ' + cmd
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return cmd
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def makepipeline(infile, steps, outfile):
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# Build a list with for each command:
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# [input filename or '', command string, kind, output filename or '']
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list = []
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for cmd, kind in steps:
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list.append(['', cmd, kind, ''])
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#
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# Make sure there is at least one step
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#
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if not list:
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list.append(['', 'cat', '--', ''])
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#
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# Take care of the input and output ends
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#
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[cmd, kind] = list[0][1:3]
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if kind[0] == 'f' and not infile:
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list.insert(0, ['', 'cat', '--', ''])
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list[0][0] = infile
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#
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[cmd, kind] = list[-1][1:3]
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if kind[1] == 'f' and not outfile:
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list.append(['', 'cat', '--', ''])
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list[-1][-1] = outfile
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#
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# Invent temporary files to connect stages that need files
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#
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garbage = []
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for i in range(1, len(list)):
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lkind = list[i-1][2]
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rkind = list[i][2]
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if lkind[1] == 'f' or rkind[0] == 'f':
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(fd, temp) = tempfile.mkstemp()
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os.close(fd)
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garbage.append(temp)
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list[i-1][-1] = list[i][0] = temp
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#
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for item in list:
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[inf, cmd, kind, outf] = item
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if kind[1] == 'f':
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cmd = 'OUT=' + quote(outf) + '; ' + cmd
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if kind[0] == 'f':
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cmd = 'IN=' + quote(inf) + '; ' + cmd
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if kind[0] == '-' and inf:
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cmd = cmd + ' <' + quote(inf)
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if kind[1] == '-' and outf:
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cmd = cmd + ' >' + quote(outf)
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item[1] = cmd
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#
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cmdlist = list[0][1]
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for item in list[1:]:
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[cmd, kind] = item[1:3]
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if item[0] == '':
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if 'f' in kind:
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cmd = '{ ' + cmd + '; }'
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cmdlist = cmdlist + ' |\n' + cmd
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else:
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cmdlist = cmdlist + '\n' + cmd
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#
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if garbage:
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rmcmd = 'rm -f'
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for file in garbage:
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rmcmd = rmcmd + ' ' + quote(file)
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trapcmd = 'trap ' + quote(rmcmd + '; exit') + ' 1 2 3 13 14 15'
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cmdlist = trapcmd + '\n' + cmdlist + '\n' + rmcmd
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#
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return cmdlist
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