当我运行setuptools.egg“好像它是一个shell脚本”时，实际发生了什么？

Question

从阅读this documentation开始，我建立了一个关于sh setuptools-0.6c11-py2.7.egg命令实际操作的心智模型，但是它非常不完整，我仍然被一些方面弄糊涂了。在

我的思维模式是这样的：

1. 当发出这个命令时，egg（我认为它是一种处理依赖关系的zip文件）会在我的系统上找到正确版本的python，并使用该python将自己“安装”到适当的位置。在
2. 实际上，这意味着一个名为easy_install的“Unix可执行文件”被创建在我的路径上。这就是为什么我可以稍后在终端中输入easy_install somepackage。在

因此，我的问题是：

1. 一个“鸡蛋”怎么能这样“自我安装”？为什么这对这个鸡蛋特别有效，当其他鸡蛋需要容易安装工作？在
2. 这样创建的“Unix可执行文件”是4kb。到底是什么？是不是充满了对其他事物的呼唤？他们在哪里？在

这不是一个'如何让它工作'的问题-我没有任何问题，沿着这条轴，但我想充分了解一下发生了什么。在

Answer 1

Egg文件是简单的压缩目录，包含Python包、模块和一些元数据，扩展名为.egg。在

zip格式是灵活的；它将忽略文件开头不属于zipfile的部分的任何内容。通过查找一系列字符（PK和另外两个表示类型的字节）并从中读取来检测zipfile。在

这意味着你可以在拉链的前面放一些东西。setuptools鸡蛋的特殊之处在于它们使用以下技巧在zip数据之前插入一些shell脚本：

$ head -n8 setuptools-0.6c11-py2.7.egg 
#!/bin/sh
if [ `basename $0` = "setuptools-0.6c11-py2.7.egg" ]
then exec python2.7 -c "import sys, os; sys.path.insert(0, os.path.abspath('$0')); from setuptools.command.easy_install import bootstrap; sys.exit(bootstrap())" "$@"
else
  echo $0 is not the correct name for this egg file.
  echo Please rename it back to setuptools-0.6c11-py2.7.egg and try again.
  exec false
fi

经过前8行，这是一个真正的拉链：

^{pr2}$

前8行中包含的脚本是运行sh setuptools-0.6c11-py2.7.egg时执行的脚本。在

如您所见，该脚本特定于egg版本；这在python2.7版本中是特定的，它只是使用python解释器将这个egg添加到python搜索路径中。然后从包含的python模块导入一个函数并运行它。在

以下是鸡蛋本身的内容，正如我所提到的，它只是一个压缩存档：

$ zipinfo -l setuptools-0.6c11-py2.7.egg 
Archive:  setuptools-0.6c11-py2.7.egg   332005 bytes   78 files
-rw-rw-r   2.0 unx     1713 b-      995 defN  7-Jul-10 20:26 site.pyc
-rw-rw-r   2.0 unx    90113 b-    31461 defN  7-Jul-10 20:26 pkg_resources.pyc
-rw-rw-r   2.0 unx    85435 b-    23537 defN 19-Oct-09 13:35 pkg_resources.py
-rw-rw-r   2.0 unx     2362 b-      875 defN 20-Sep-06 17:05 site.py
-rw-rw-r   2.0 unx      309 b-      224 defN  7-Jul-10 20:26 easy_install.pyc
-rw-rw-r   2.0 unx      126 b-      105 defN 20-Sep-06 17:05 easy_install.py
-rw-rw-r   2.0 unx       43 b-       43 defN  7-Jul-10 20:26 EGG-INFO/top_level.txt
-rw-rw-r   2.0 unx     1591 b-      458 defN  7-Jul-10 20:26 EGG-INFO/SOURCES.txt
-rw-rw-r   2.0 unx        1 b-        3 defN 20-Oct-09 10:07 EGG-INFO/zip-safe
-rw-rw-r   2.0 unx     9278 b-     3194 defN  7-Jul-10 20:26 EGG-INFO/PKG-INFO
-rwxrwxr-x  2.0 unx     2504 b-      623 defN  7-Jul-10 20:26 EGG-INFO/entry_points.txt
-rw-rw-r   2.0 unx        1 b-        3 defN  7-Jul-10 20:26 EGG-INFO/dependency_links.txt
-rw-rw-r   2.0 unx     1567 b-      791 defN  7-Jul-10 20:26 setuptools/extension.pyc
-rw-rw-r   2.0 unx     1089 b-      424 defN 20-Sep-06 17:05 setuptools/extension.py
-rw-rw-r   2.0 unx    10796 b-     4050 defN  7-Jul-10 20:26 setuptools/sandbox.pyc
-rw-rw-r   2.0 unx     8227 b-     2309 defN  6-Jul-10 20:09 setuptools/sandbox.py
-rw-rw-r   2.0 unx     5677 b-     2499 defN  7-Jul-10 20:26 setuptools/archive_util.pyc
-rw-rw-r   2.0 unx    26800 b-    11228 defN  7-Jul-10 20:26 setuptools/package_index.pyc
-rw-rw-r   2.0 unx     6209 b-     2229 defN 19-Oct-09 13:35 setuptools/depends.py
-rw-rw-r   2.0 unx     6677 b-     3096 defN  7-Jul-10 20:26 setuptools/depends.pyc
-rw-rw-r   2.0 unx     2816 b-     1159 defN  6-Jul-10 20:09 setuptools/__init__.py
-rw-rw-r   2.0 unx     3639 b-     1837 defN  7-Jul-10 20:26 setuptools/__init__.pyc
-rw-rw-r   2.0 unx     5924 b-     1777 defN 19-Oct-09 13:35 setuptools/archive_util.py
-rw-rw-r   2.0 unx    29972 b-     8156 defN 19-Oct-09 13:35 setuptools/dist.py
-rwxrwxr-x  2.0 unx     7168 b-     3249 defN 19-Oct-09 17:18 setuptools/cli.exe
-rw-rw-r   2.0 unx    28275 b-     8698 defN  6-Jul-10 20:09 setuptools/package_index.py
-rw-rw-r   2.0 unx    29786 b-    10953 defN  7-Jul-10 20:26 setuptools/dist.pyc
-rwxrwxr-x  2.0 unx     7168 b-     3244 defN 19-Oct-09 17:18 setuptools/gui.exe
-rw-rw-r   2.0 unx    22219 b-     7042 defN  7-Jul-10 20:26 setuptools/tests/test_resources.pyc
-rw-rw-r   2.0 unx    19388 b-     4723 defN 24-Sep-08 13:10 setuptools/tests/test_resources.py
-rw-rw-r   2.0 unx    12345 b-     2765 defN 24-Sep-08 13:10 setuptools/tests/__init__.py
-rw-rw-r   2.0 unx    13811 b-     4523 defN  7-Jul-10 20:26 setuptools/tests/__init__.pyc
-rw-rw-r   2.0 unx     1499 b-      708 defN  7-Jul-10 20:26 setuptools/tests/test_packageindex.pyc
-rw-rw-r   2.0 unx    81351 b-    27171 defN  7-Jul-10 20:26 setuptools/tests/doctest.pyc
-rw-rw-r   2.0 unx      759 b-      346 defN 24-Sep-08 13:10 setuptools/tests/test_packageindex.py
-rw-rw-r   2.0 unx    99714 b-    25663 defN 20-Sep-06 17:05 setuptools/tests/doctest.py
-rw-rw-r   2.0 unx     2866 b-     1332 defN  7-Jul-10 20:26 setuptools/command/rotate.pyc
-rw-rw-r   2.0 unx    11520 b-     3127 defN 19-Oct-09 13:35 setuptools/command/build_ext.py
-rw-rw-r   2.0 unx     6649 b-     2208 defN 24-Sep-08 13:10 setuptools/command/upload.py
-rw-rw-r   2.0 unx     8162 b-     3538 defN  7-Jul-10 20:26 setuptools/command/sdist.pyc
-rw-rw-r   2.0 unx     5965 b-     2421 defN  7-Jul-10 20:26 setuptools/command/setopt.pyc
-rw-rw-r   2.0 unx     2283 b-      695 defN 19-Oct-09 17:50 setuptools/command/bdist_wininst.py
-rw-rw-r   2.0 unx     7535 b-     3208 defN  7-Jul-10 20:26 setuptools/command/build_py.pyc
-rw-rw-r   2.0 unx     3690 b-     1528 defN  7-Jul-10 20:26 setuptools/command/install.pyc
-rw-rw-r   2.0 unx    14205 b-     4465 defN 19-Oct-09 13:35 setuptools/command/egg_info.py
-rw-rw-r   2.0 unx      626 b-      311 defN 28-Dec-06 19:52 setuptools/command/__init__.py
-rw-rw-r   2.0 unx      839 b-      494 defN  7-Jul-10 20:26 setuptools/command/__init__.pyc
-rw-rw-r   2.0 unx     5053 b-     1519 defN 20-Sep-06 17:05 setuptools/command/setopt.py
-rw-rw-r   2.0 unx      674 b-      329 defN  7-Jul-10 20:26 setuptools/command/register.pyc
-rw-rw-r   2.0 unx     3724 b-     1292 defN  4-Sep-07 00:11 setuptools/command/install_egg_info.py
-rw-rw-r   2.0 unx    18005 b-     5444 defN 19-Oct-09 13:35 setuptools/command/bdist_egg.py
-rw-rw-r   2.0 unx     3984 b-     1385 defN 15-Feb-08 12:29 setuptools/command/install.py
-rw-rw-r   2.0 unx     2356 b-     1002 defN  7-Jul-10 20:26 setuptools/command/bdist_wininst.pyc
-rw-rw-r   2.0 unx     2025 b-      774 defN 22-May-07 17:55 setuptools/command/bdist_rpm.py
-rw-rw-r   2.0 unx     2486 b-      871 defN 20-Sep-06 17:05 setuptools/command/install_lib.py
-rw-rw-r   2.0 unx      740 b-      357 defN 20-Sep-06 17:05 setuptools/command/saveopts.py
-rw-rw-r   2.0 unx    56980 b-    23198 defN  7-Jul-10 20:26 setuptools/command/easy_install.pyc
-rw-rw-r   2.0 unx     3172 b-     1438 defN  7-Jul-10 20:26 setuptools/command/install_lib.pyc
-rw-rw-r   2.0 unx     2257 b-     1013 defN  7-Jul-10 20:26 setuptools/command/bdist_rpm.pyc
-rw-rw-r   2.0 unx     5310 b-     1732 defN 15-Feb-08 12:29 setuptools/command/develop.py
-rw-rw-r   2.0 unx     5091 b-     2222 defN  7-Jul-10 20:26 setuptools/command/test.pyc
-rw-rw-r   2.0 unx    63580 b-    17507 defN 19-Oct-09 13:35 setuptools/command/easy_install.py
-rw-rw-r   2.0 unx    16467 b-     6544 defN  7-Jul-10 20:26 setuptools/command/egg_info.pyc
-rw-rw-r   2.0 unx     4577 b-     1994 defN  7-Jul-10 20:26 setuptools/command/install_egg_info.pyc
-rw-rw-r   2.0 unx     6275 b-     3108 defN  7-Jul-10 20:26 setuptools/command/upload.pyc
-rw-rw-r   2.0 unx     7246 b-     2237 defN 20-Sep-06 17:05 setuptools/command/build_py.py
-rw-rw-r   2.0 unx    10073 b-     4314 defN  7-Jul-10 20:26 setuptools/command/build_ext.pyc
-rw-rw-r   2.0 unx     3185 b-     1463 defN  7-Jul-10 20:26 setuptools/command/alias.pyc
-rw-rw-r   2.0 unx     1921 b-      704 defN 15-Feb-08 12:29 setuptools/command/install_scripts.py
-rw-rw-r   2.0 unx     7327 b-     2380 defN 19-Oct-09 15:46 setuptools/command/sdist.py
-rw-rw-r   2.0 unx     1249 b-      647 defN  7-Jul-10 20:26 setuptools/command/saveopts.pyc
-rw-rw-r   2.0 unx     2021 b-      750 defN 20-Sep-06 17:05 setuptools/command/rotate.py
-rw-rw-r   2.0 unx     2477 b-      848 defN 19-Oct-09 13:35 setuptools/command/alias.py
-rw-rw-r   2.0 unx    17695 b-     7800 defN  7-Jul-10 20:26 setuptools/command/bdist_egg.pyc
-rw-rw-r   2.0 unx      277 b-      158 defN 20-Sep-06 17:05 setuptools/command/register.py
-rw-rw-r   2.0 unx     4442 b-     1424 defN 15-Feb-08 12:29 setuptools/command/test.py
-rw-rw-r   2.0 unx     2445 b-     1160 defN  7-Jul-10 20:26 setuptools/command/install_scripts.pyc
-rw-rw-r   2.0 unx     5175 b-     2317 defN  7-Jul-10 20:26 setuptools/command/develop.pyc
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