用空格缩进heredocs [英] Indenting heredocs with spaces

问题描述

对于我从事的个人开发和项目，我们使用四个空格代替制表符. 但是，我需要使用Heredoc，并且我必须在不中断缩进流程的情况下使用它.

For personal development and projects I work on, we use four spaces instead of tabs. However, I need to use a heredoc, and I can't do so without breaking the indention flow.

我能想到的唯一可行的方法是:

The only working way to do this I can think of would be this:

usage() {
    cat << '    EOF' | sed -e 's/^    //';
    Hello, this is a cool program.
    This should get unindented.
    This code should stay indented:
        something() {
            echo It works, yo!;
        }
    That's all.
    EOF
}

有更好的方法吗?

让我知道它是否属于 Unix/Linux Stack Exchange .

推荐答案

(如果您使用的是bash 4，请滚动到最后，我认为这是纯shell和可读性的最佳组合.)

(If you are using bash 4, scroll to the end for what I think is the best combination of pure shell and readability.)

对于shell脚本，使用制表符不是偏好或样式的问题；这就是语言的定义方式.

For shell scripts, using tabs is not a matter of preference or style; it's how the language is defined.

usage () {
⟶# Lines between EOF are each indented with the same number of tabs
⟶# Spaces can follow the tabs for in-document indentation
⟶cat <<-EOF
⟶⟶Hello, this is a cool program.
⟶⟶This should get unindented.
⟶⟶This code should stay indented:
⟶⟶    something() {
⟶⟶        echo It works, yo!;
⟶⟶    }
⟶⟶That's all.
⟶EOF
}

另一种选择是完全避免使用此处的文档，但必须使用更多的引号和换行符:

Another option is to avoid a here document altogether, at the cost of having to use more quotes and line continuations:

usage () {
    printf '%s\n' \
        "Hello, this is a cool program." \
        "This should get unindented." \
        "This code should stay indented:" \
        "    something() {" \
        "        echo It works, yo!" \
        "    }" \
        "That's all."
}

如果您愿意放弃POSIX兼容性，则可以使用数组来避免显式的行继续:

If you are willing to forego POSIX compatibility, you can use an array to avoid the explicit line continuations:

usage () {
    message=(
        "Hello, this is a cool program."
        "This should get unindented."
        "This code should stay indented:"
        "    something() {"
        "        echo It works, yo!"
        "    }"
        "That's all."
    )
    printf '%s\n' "${message[@]}"
}

---

以下内容再次使用here文档，但是这次使用bash 4的readarray命令填充数组.参数扩展用于从每个谎言的开头删除固定数量的空格.

---

The following uses a here document again, but this time with bash 4's readarray command to populate an array. Parameter expansion takes care of removing a fixed number of spaces from the beginning of each lie.

usage () {
    # No tabs necessary!
    readarray message <<'    EOF'
        Hello, this is a cool program.
        This should get unindented.
        This code should stay indented:
            something() {
                echo It works, yo!;
            }
        That's all.
    EOF
    # Each line is indented an extra 8 spaces, so strip them
    printf '%s' "${message[@]#        }"
}

最后一个变体:您可以使用扩展模式来简化参数扩展.不必计算缩进使用了多少空格，只需以所选的非空格字符结束缩进，然后匹配固定前缀即可.我使用:. (以下空格 冒号是为了提高可读性；只需稍加更改前缀模式就可以删除它.)

One last variation: you can use an extended pattern to simplify the parameter expansion. Instead of having to count how many spaces are used for indentation, simply end the indentation with a chosen non-space character, then match the fixed prefix. I use :. (The space following the colon is for readability; it can be dropped with a minor change to the prefix pattern.)

(此外，使用以空格开头的here-doc分隔符的一个很好的技巧的一个缺点是，它会阻止您在here-doc内执行扩展.如果您想这样做，您可以要么必须保留定界符不缩进，要么对您的无制表符规则做一个小小的例外，并使用<<-EOF和制表符为缩进的结束定界符.)

(Also, as an aside, one drawback to your very nice trick of using a here-doc delimiter that starts with whitespace is that it prevents you from performing expansions inside the here-doc. If you wanted to do so, you'd have to either leave the delimiter unindented, or make one minor exception to your no-tab rule and use <<-EOF and a tab-indented closing delimiter.)

usage () {
    # No tabs necessary!
    closing="That's all"
    readarray message <<EOF
       : Hello, this is a cool program.
       : This should get unindented.
       : This code should stay indented:
       :      something() {
       :          echo It works, yo!;
       :      }
       : $closing
EOF
    shopt -s extglob
    printf '%s' "${message[@]#+( ): }"
    shopt -u extglob
}

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