[Martin v. Löwis]
> ...
> Can somebody remember what the reason is to invoke cmd.exe (or COMSPEC)
> in os.popen?
Absolutely necessary, as any number of shell gimmicks can be used in
the passed string, same as on non-Windows boxes; .e.g.,
>>> import os
>>> os.environ['STR'] = 'SSL'
>>> p = os.popen("findstr %STR% *.py | sort")
>>> print p.read()
build_ssl.py: print " None of these versions appear suitable
for building OpenSSL"
build_ssl.py: print "Could not find an SSL directory in '%s'" %
(sources,)
build_ssl.py: print "Found an SSL directory at '%s'" % (best_name,)
build_ssl.py: # Look for SSL 2 levels up from pcbuild - ie, same
place zlib etc all live.
...
That illustrates envar substitution and setting up a pipe in the
passed string, and people certainly do things like that.
These are the MS docs for cmd.exe's inscrutable quoting rules after /C:
"""
If /C or /K is specified, then the remainder of the command line after
the switch is processed as a command line, where the following logic is
used to process quote (") characters:
1. If all of the following conditions are met, then quote characters
on the command line are preserved:
- no /S switch
- exactly two quote characters
- no special characters between the two quote characters,
where special is one of: &<>()@^|
- there are one or more whitespace characters between the
the two quote characters
- the string between the two quote characters is the name
of an executable file.
2. Otherwise, old behavior is to see if the first character is
a quote character and if so, strip the leading character and
remove the last quote character on the command line, preserving
any text after the last quote character.
"""
Your
cmd.exe /c "c:\Program Files\python25\python.exe"
example fit clause #1 above.
cmd.exe /c "c:\Program Files\python25\python.exe" -c "import sys;print
sys.version"
fails the "exactly two quote characters" part of #1, so falls into #2,
and after stripping the first and last quotes leaves the senseless:
cmd.exe /c c:\Program Files\python25\python.exe" -c "import sys;print
sys.version
> (i.e. doubling the quotes at the beginning and the end) [works]
And that follows from the above, although not for a reason any sane
person would guess :-(
I personally wouldn't change anything here for 2.5. It's a minefield,
and people who care a lot already have their own workarounds in place,
which we'd risk breaking. It remains a minefield for newbies, but
we're really just passing on cmd.exe's behaviors. People are
well-advised to accept the installer's default directory.
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