我应该在环境路径名中使用引号吗? [英] Should I use quotes in environment path names?

问题描述

我正在清理我的所有配置文件，以使它们尽可能可读.我一直在寻找在导出~/.bashrc文件中的路径时使用引号的样式指南:

I'm in the process of cleaning up all my config files in an attempt to make them as readable as possible. I've been looking for a style guide on the use of quotes while exporting paths in, for example, a ~/.bashrc file:

export PATH="/users/me/path:$PATH"

vs

export PATH=/users/me/path:$PATH

Google 外壳样式指南建议避免使用路径名引号.相比之下，很多流行的点文件存储库(例如Zach Holman的在此)使用引号.在路径中使用引号是否有优势?

The Google shell style guide suggests avoiding quotes for path names. In contrast, a lot of the popular dotfiles repos (such as Zach Holman's here) use quotes. Are there any situations when it is an advantage to use quotes in the path?

推荐答案

^{帽子提示到 @gniourf_gniourf 和 @chepner 寻求帮助.}

^{Tip of the hat to @gniourf_gniourf and @chepner for their help.}

tl;博士

为安全起见，请双引号:在所有情况下，它都适用于所有类似POSIX的外壳.

如果要添加基于~的路径，请选择性地保留~/ 不带引号的，以确保扩展~；例如:export PATH=~/"bin:$PATH". ^{有关变量分配中~扩展的规则，请参见下文.}
或者，只需在单个双引号字符串内使用$HOME:
export PATH="$HOME/bin:$PATH"

If you want to add a ~-based path, selectively leave the ~/ unquoted to ensure that ~ is expanded; e.g.: export PATH=~/"bin:$PATH". ^{See below for the rules of ~ expansion in variable assignments.}
Alternatively, simply use $HOME inside a single, double-quoted string:
export PATH="$HOME/bin:$PATH"

注意:以下内容适用于 bash，ksh和zsh ，但不适用于(大部分)严格符合POSIX的外壳，例如dash；因此，在定位/bin/sh时，必须将export 的RHS放在双引号中. ^[1]

NOTE: The following applies to bash, ksh, and zsh, but NOT to (mostly) strictly POSIX compliant shells such as dash; thus, when you target /bin/sh, you MUST double-quote the RHS of export.^[1]

• 双引号是 可选，仅当RHS的 literal 部分(要分配的值)不包含空格或其他外壳元字符时.
• 所引用的变量的值是否包含空格/元字符无关无关紧要-参见下文.
  • 同样:使用export时，与sh有关系，因此请始终在其中双引号.
  • Double-quotes are optional, ONLY IF the literal part of your RHS (the value to assign) contains neither whitespace nor other shell metacharacters.
  • Whether the values of the variables referenced contain whitespace/metacharacters or not does not matter - see below.
    • Again: It does matter with sh, when export is used, so always double-quote there.

    在这种情况下无需双引号就可以逃脱的原因是，像POSIX的shell中的 variable-assignment 语句与 arguments 传递给 commands ，如

    The reason you can get away without double-quoting in this case is that variable-assignment statements in POSIX-like shells interpret their RHS differently than arguments passed to commands, as described in section 2.9.1 of the POSIX spec:

    • 具体地说，即使执行了初始分词 ，它也仅适用于未扩展(原始)RHS(这就是为什么您要做需要用 literals 中的空格/元字符引用)，而不是引用其结果.

    • Specifically, even though initial word-splitting is performed, it is only applied to the unexpanded (raw) RHS (that's why you do need quoting with whitespace/metacharacters in literals), and not to its results.

    此仅适用于形式为
    的真正赋值语句 所有类似于POSIX的外壳中的<name>=<value> ，即，如果变量名称前没有命令名称；请注意，其中包括对命令的前缀赋值，以为其定义临时环境变量，例如foo=$bar cmd ....

    This only applies to genuine assignment statements of the form
    <name>=<value> in all POSIX-like shells, i.e., if there is no command name before the variable name; note that that includes assignments prepended to a command to define ad-hoc environment variables for it, e.g., foo=$bar cmd ....

    在其他命令上下文中的赋值 应该始终加双引号.

    Assignments in the context of other commands should always be double-quoted, to be safe:

    • 使用sh(在(大多数情况下)严格符合POSIX的外壳程序中，例如dash)中，将export的赋值视为常规命令，而foo=$bar部分被视为内置export的第一个参数，因此也照常进行处理(也受制于结果的分词).
      (POSIX没有指定任何其他涉及(显式)变量分配的命令； declare，typeset和local是非标准的扩展名).

    • With sh (in a (mostly) strictly POSIX-compliant shell such as dash) an assignment with export is treated as a regular command, and the foo=$bar part is treated as the 1st argument to the export builtin and therefore treated as usual (subject to word-splitting of the result, too).
      (POSIX doesn't specify any other commands involving (explicit) variable-assignment; declare, typeset, and local are nonstandard extensions).

    bash，ksh，zsh与POSIX可以理解的偏差是，也将分配逻辑扩展到export foo=$bar和typeset/declare/local foo=$bar.换句话说:bash，ksh，zsh，export/typeset/declare/local命令中的就像 assignments 一样对待，因此不必严格引用..

    bash, ksh, zsh, in an understandable deviation from POSIX, extend the assignment logic to export foo=$bar and typeset/declare/local foo=$bar as well. In other words: in bash, ksh, zsh, export/typeset/declare/local commands are treated like assignments, so that quoting isn't strictly necessary.

    • 令人惊讶的是，dash，它也选择实现了 non -POSIX local内置 ^[2] ，不向其扩展分配逻辑；但是，它与其export行为一致.
    • Perhaps surprisingly, dash, which also chose to implement the non-POSIX local builtin^[2] , does NOT extend assignment logic to it; it is consistent with its export behavior, however.

    传递给env的赋值(例如env foo=$bar cmd ...)也可以作为命令参数进行扩展，因此需要双引号-除zsh以外.

    Assignments passed to env (e.g., env foo=$bar cmd ...) are also subject to expansion as a command argument and therefore need double-quoting - except in zsh.

    • 在这方面，env与ksh和bash中的export行为不同是由于以下事实:env是外部实用程序，而export是内置的 shell .
      (对于未加引号的变量引用，zsh的行为根本上与其他shell的行为不同.)
    • That env acts differently from export in ksh and bash in that regard is due to the fact that env is an external utility, whereas export is a shell builtin.
      (zsh's behavior fundamentally differs from that of the other shells when it comes to unquoted variable references).

    波浪号(~)扩展在真正赋值语句中发生:

    Tilde (~) expansion happens as follows in genuine assignment statements:

    • 除了~不需要被引用以外，它通常也仅适用于:
      • 如果整个 RHS为~；例如.:
        • foo=~ # same as: foo="$HOME"
        • In addition to the ~ needing to be unquoted, as usual, it is also only applied:
          • If the entire RHS is ~; e.g.:
            • foo=~ # same as: foo="$HOME"
            • 如果~以字符串开头或以不带引号的 :
            • 如果~后跟不带引号的 /.
            • 例如，
              foo=~/bin # same as foo="$HOME/bin"
foo=$foo:~/bin # same as foo="$foo:$HOME/bin"
            • if ~ starts the string or is preceded by an unquoted :
            • if ~ is followed by an unquoted /.
            • e.g.,
              foo=~/bin # same as foo="$HOME/bin"
foo=$foo:~/bin # same as foo="$foo:$HOME/bin"

            示例

            此示例说明，在bash，ksh和zsh中，即使使用export，您也可以不用双引号而忽略，但是我不这样做推荐.

            This example demonstrates that in bash, ksh, and zsh you can get away without double-quoting, even when using export, but I do not recommend it.

            #!/usr/bin/env bash
            # or ksh or zsh - but NOT /bin/sh!
            
            # Create env. variable with whitespace and other shell metacharacters
            export FOO="b:c &|<> d"
            
            # Extend the value - the double quotes here are optional, but ONLY 
            # because the literal part, 'a:`, contains no whitespace or other shell metacharacters.
            # To be safe, DO double-quote the RHS.
            export FOO=a:$foo # OK - $FOO now contains 'a:b:c &|<> d'
            

            ---

            ^{[1]正如@gniourf_gniourf指出的:使用export来修改 值是PATH是可选的，因为一旦将变量标记为已导出，就可以使用常规分配(PATH=...)来更改其值.
            也就是说，您仍然可以选择以使用export，以便明确指出要修改的变量已导出.}

            ---

            ^{[1] As @gniourf_gniourf points out: Use of export to modify the value of PATH is optional, because once a variable is marked as exported, you can use a regular assignment (PATH=...) to change its value.
            That said, you may still choose to use export, so as to make it explicit that the variable being modified is exported.}

            ^{[2] @gniourf_gniourf指出，POSIX标准的未来版本可能会引入内置的local.}

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