当运行zsh -l -c＆＃39; echo＆＃34; __ $ {PATH} __＆＃34;＆＃39;时，virtualenv目录转移到$ PATH的末尾。

Question

为什么virtualenv路径在最后一个命令中移到了最后？

Last login: Tue Aug 26 19:14:49 on ttys000
➜  ~  echo $PATH
/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin
➜  ~  zsh -l -c 'echo "__${PATH}__"'
__/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin__
➜  ~  . ./venvs/py_venv/bin/activate
(py_venv)➜  ~  echo $PATH
/Users/aj/venvs/py_venv/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin
(py_venv)➜  ~  zsh -l -c 'echo "__${PATH}__"'
__/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin:/Users/aj/venvs/py_venv/bin__
(py_venv)➜  ~

修改

进一步调查似乎表明它与单引号和双引号有关。仍不确定原因：

(py_venv)➜  ~  zsh -l -c "echo $PATH"
/Users/aj/venvs/py_venv/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin
(py_venv)➜  ~  zsh -l -c 'echo $PATH'
/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin:/Users/aj/venvs/py_venv/bin

Answer 1

在我的（ Ubuntu ） zsh 环境中，我没有看到行为上的差异，但我怀疑你的情况（可能与 OS X ）它可能与双引号允许完全替换这一事实有关，而单引号则不然。

例如，如果运行echo '$PATH'，它将输出$PATH，而echo "$PATH"将环境变量的值替换为echo命令并输出完整路径。 / p>

Further reading on zsh quoting

修改

我尝试了一些你的确切zsh命令的变体，并且可以重现类似的东西，虽然我最终没有输出而不是它转移到最后：

 (venv_test) ~  zsh -l -c 'echo "__$PATH__"'
__
 (venv_test) ~  zsh -l -c 'echo __$PATH__' 
__
 (venv_test) ~  zsh -l -c "echo __$PATH__"
__
 (venv_test) ~  zsh -l -c "echo __${PATH}__"
__/home/khampson/virtualenvs/venv_test/bin:/home/khampson/bin__

尝试在env var周围使用花括号切换到双引号（我怀疑尾部下划线被视为env var名称的一部分）。

Answer 2

来自zsh手册页：

STARTUP/SHUTDOWN FILES
       Commands are first read from /etc/zshenv; this cannot be overridden....

所以，让我们默认看看Mac OS X在那里有什么：

➜  ~  cat /etc/zshenv
# system-wide environment settings for zsh(1)
if [ -x /usr/libexec/path_helper ]; then
    eval `/usr/libexec/path_helper -s`
fi

好的，/usr/libexec/path_helper是什么？

➜  ~  man path_helper
DESCRIPTION
     The path_helper utility reads the contents of the files in the directories /etc/paths.d and /etc/manpaths.d and appends their contents to the PATH and MANPATH environment variables respectively.

因此，如果path_helper 附加 ，那么为什么将venv目录推送到最后？答案是它没有附加，它预先添加，文档不正确。它似乎也在做一些重复推理：

(py_venv)➜  ~  echo $PATH
/Users/aj/venvs/py_venv/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin
(py_venv)➜  ~  /usr/libexec/path_helper -s
PATH="/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin:/Users/aj/venvs/py_venv/bin"; export PATH;
(py_venv)➜  ~  PATH="" /usr/libexec/path_helper -s
PATH="/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin"; export PATH;
(py_venv)➜  ~  PATH="/foo/bar" /usr/libexec/path_helper -s
PATH="/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin:/foo/bar"; export PATH;
(py_venv)➜  ~  PATH="/foo/bar:/usr/bin:/usr/local/bin" /usr/libexec/path_helper -s
PATH="/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin:/foo/bar"; export PATH;
(py_venv)➜  ~