更新
一个简单的问题。假设一个名为“unpack.py”的脚本将“inputfile.gz”放入stdout而不是使用以下命令创建“output.gz”： -
python unpack.py inputfile.gz
是否可以通过使用以下命令重定向stdout来创建“output.gz”？
python unpack.py inputfile.gz > outputfile.gz
重定向后，是"inputfile.gz" == "outputfile.gz"？
UPDATE2
它似乎确实创建“outputfile.gz”。经过file检查，之前和之后似乎相同。
$ file core.gz
core.gz: gzip compressed data, was "core.cpio", from Unix, last modified: Sat Feb 18 22:22:16 2012, max compression
[sundar@localhost multibootusb]$ file core-redirect.gz
core-redirect.gz: gzip compressed data, was "core.cpio", from Unix, last modified: Sat Feb 18 22:22:16 2012, max compression
但是，当我尝试再次提取这两个文件时，重定向的文件似乎没有按预期工作并引发错误gzip: core-redirect.gz: unexpected end of file
$ gunzip core-redirect.gz
gzip: core-redirect.gz: unexpected end of file
$ gunzip core.gz
$
我的实际问题如下......
我一直在尝试使用barneygale编写的github上的python脚本列出并提取iso。实际的脚本在这里： -
import urllib
import struct
try:
from cStringIO import StringIO
except ImportError:
from StringIO import StringIO
class ISO9660IOError(IOError):
def __init__(self, path):
self.path = path
def __str__(self):
return "Path not found: %s" % self.path
class ISO9660(object):
def __init__(self, url):
self._buff = None #input buffer
self._root = None #root node
self._pvd = {} #primary volume descriptor
self._paths = [] #path table
self._url = url
self._get_sector = self._get_sector_url if url.startswith('http') else self._get_sector_file
### Volume Descriptors
sector = 0x10
while True:
self._get_sector(sector, 2048)
sector += 1
ty = self._unpack('B')
if ty == 1:
self._unpack_pvd()
elif ty == 255:
break
else:
continue
### Path table
l0 = self._pvd['path_table_size']
self._get_sector(self._pvd['path_table_l_loc'], l0)
while l0 > 0:
p = {}
l1 = self._unpack('B')
l2 = self._unpack('B')
p['ex_loc'] = self._unpack('<I')
p['parent'] = self._unpack('<H')
p['name'] = self._unpack_string(l1)
if l1%2 == 1:
self._unpack('B')
self._paths.append(p)
l0 -= 8 + l1 + (l1 % 2)
assert l0 == 0
##
## Generator listing available files/folders
##
def tree(self, get_files = True):
if get_files:
gen = self._tree_node(self._root)
else:
gen = self._tree_path('', 1)
yield '/'
for i in gen:
yield i
def _tree_path(self, name, index):
spacer = lambda s: "%s/%s" % (name, s)
for i, c in enumerate(self._paths):
if c['parent'] == index and c['name'] not in '\x00\x01':
yield spacer(c['name'])
for d in self._tree_path(spacer(c['name']), i+1):
yield d
def _tree_node(self, node):
spacer = lambda s: "%s/%s" % (node['name'].lstrip('\x00\x01'), s)
for c in list(self._unpack_dir_children(node)):
yield spacer(c['name'])
if c['flags'] & 2:
for d in self._tree_node(c):
yield spacer(d)
##
## Retrieve file contents as a string
##
def get_file(self, path):
path = path.upper().strip('/').split('/')
path, filename = path[:-1], path[-1]
if len(path)==0:
parent_dir = self._root
else:
try:
parent_dir = self._dir_record_by_table(path)
except ISO9660IOError:
parent_dir = self._dir_record_by_root(path)
f = self._search_dir_children(parent_dir, filename)
self._get_sector(f['ex_loc'], f['ex_len'])
return self._unpack_raw(f['ex_len'])
##
## Methods for retrieving partial contents
##
def _get_sector_url(self, sector, length):
start = sector * 2048
if self._buff:
self._buff.close()
opener = urllib.FancyURLopener()
opener.http_error_206 = lambda *a, **k: None
opener.addheader("Range", "bytes=%d-%d" % (start, start+length-1))
self._buff = opener.open(self._url)
def _get_sector_file(self, sector, length):
with open(self._url, 'rb') as f:
f.seek(sector*2048)
self._buff = StringIO(f.read(length))
##
## Return the record for final directory in a path
##
def _dir_record_by_table(self, path):
for e in self._paths[::-1]:
search = list(path)
f = e
while f['name'] == search[-1]:
search.pop()
f = self._paths[f['parent']-1]
if f['parent'] == 1:
e['ex_len'] = 2048 #TODO
return e
raise ISO9660IOError(path)
def _dir_record_by_root(self, path):
current = self._root
remaining = list(path)
while remaining:
current = self._search_dir_children(current, remaining[0])
remaining.pop(0)
return current
##
## Unpack the Primary Volume Descriptor
##
def _unpack_pvd(self):
self._pvd['type_code'] = self._unpack_string(5)
self._pvd['standard_identifier'] = self._unpack('B')
self._unpack_raw(1) #discard 1 byte
self._pvd['system_identifier'] = self._unpack_string(32)
self._pvd['volume_identifier'] = self._unpack_string(32)
self._unpack_raw(8) #discard 8 bytes
self._pvd['volume_space_size'] = self._unpack_both('i')
self._unpack_raw(32) #discard 32 bytes
self._pvd['volume_set_size'] = self._unpack_both('h')
self._pvd['volume_seq_num'] = self._unpack_both('h')
self._pvd['logical_block_size'] = self._unpack_both('h')
self._pvd['path_table_size'] = self._unpack_both('i')
self._pvd['path_table_l_loc'] = self._unpack('<i')
self._pvd['path_table_opt_l_loc'] = self._unpack('<i')
self._pvd['path_table_m_loc'] = self._unpack('>i')
self._pvd['path_table_opt_m_loc'] = self._unpack('>i')
d, self._root = self._unpack_record() #root directory record
self._pvd['volume_set_identifer'] = self._unpack_string(128)
self._pvd['publisher_identifier'] = self._unpack_string(128)
self._pvd['data_preparer_identifier'] = self._unpack_string(128)
self._pvd['application_identifier'] = self._unpack_string(128)
self._pvd['copyright_file_identifier'] = self._unpack_string(38)
self._pvd['abstract_file_identifier'] = self._unpack_string(36)
self._pvd['bibliographic_file_identifier'] = self._unpack_string(37)
self._pvd['volume_datetime_created'] = self._unpack_vd_datetime()
self._pvd['volume_datetime_modified'] = self._unpack_vd_datetime()
self._pvd['volume_datetime_expires'] = self._unpack_vd_datetime()
self._pvd['volume_datetime_effective'] = self._unpack_vd_datetime()
self._pvd['file_structure_version'] = self._unpack('B')
##
## Unpack a directory record (a listing of a file or folder)
##
def _unpack_record(self):
l0 = self._unpack('B')
if l0 == 0: return 1, None
l1 = self._unpack('B')
d = dict()
d['ex_loc'] = self._unpack_both('I')
d['ex_len'] = self._unpack_both('I')
d['datetime'] = self._unpack_dir_datetime()
d['flags'] = self._unpack('B')
d['interleave_unit_size'] = self._unpack('B')
d['interleave_gap_size'] = self._unpack('B')
d['volume_sequence'] = self._unpack_both('h')
l2 = self._unpack('B')
d['name'] = self._unpack_string(l2).split(';')[0]
if l2 % 2 == 0:
self._unpack('B')
t = 34 + l2 - (l2 % 2)
e = l0-t
if e>0:
extra = self._unpack_raw(e)
return l0, d
#Assuming d is a directory record, this generator yields its children
def _unpack_dir_children(self, d):
read = 0
self._get_sector(d['ex_loc'], d['ex_len'])
while read < d['ex_len']: #Iterate over files in the directory
data, e = self._unpack_record()
read += data
if data == 1: #end of directory listing
break
if e['name'] not in '\x00\x01':
yield e
#Search for one child amongst the children
def _search_dir_children(self, d, term):
for e in self._unpack_dir_children(d):
if e['name'] == term:
return e
raise ISO9660IOError(term)
##
## Datatypes
##
def _unpack_raw(self, l):
return self._buff.read(l)
#both-endian
def _unpack_both(self, st):
a = self._unpack('<'+st)
b = self._unpack('>'+st)
assert a == b
return a
def _unpack_string(self, l):
return self._buff.read(l).rstrip(' ')
def _unpack(self, st):
if st[0] not in ('<','>'):
st = '<' + st
d = struct.unpack(st, self._buff.read(struct.calcsize(st)))
if len(st) == 2:
return d[0]
else:
return d
def _unpack_vd_datetime(self):
return self._unpack_raw(17) #TODO
def _unpack_dir_datetime(self):
return self._unpack_raw(7) #TODO
if __name__ == '__main__':
import sys
if len(sys.argv) < 2:
print "usage: python iso9660.py isourl [path]"
else:
iso_path = sys.argv[1]
ret_path = sys.argv[2] if len(sys.argv) > 2 else None
cd = ISO9660(iso_path)
if ret_path:
print cd.get_file(ret_path)
else:
for path in cd.tree():
print path
#print cd.get_file('md5sum.txt')
脚本几乎接近我想要的。它可以列出一个iso。例如： -
$ python ./iso9660.py aTinyCore-4.3.iso
/
/BOOT
/BOOT/CORE.GZ
/BOOT/ISOLINUX
/BOOT/ISOLINUX/BOOT.CAT
/BOOT/ISOLINUX/BOOT.MSG
/BOOT/ISOLINUX/F2.
/BOOT/ISOLINUX/F3.
/CDE/XBASE.LST
但是，它不支持直接提取iso文件。相反，如果提供了驻留在iso中的文件路径，它会将所有数据/二进制文件写入stdout。
例如： -
$ python ./iso9660.py aTinyCore-4.3.iso /BOOT/ISOLINUX/ISOLINUX.CFG
display boot.msg
default tc
label tc
kernel /boot/vmlinuz
append initrd=/boot/core.gz quiet cde
F4 f4
我现在的问题是，是否可以将这些stdout写入文件（如果stdout内容是文件）/ data（如果stdout内容是数据）/ binary（如果stdout内容是二进制），那么内容可以提取iso？ python是否将文件和二进制文件的stdout相同？
高度赞赏任何领先的问题。