Shell 脚本 Bash，检查字符串是否以单引号开头和结尾

Shell script Bash, Check if string starts and ends with single quotes

提问by chichi

I need to check if a string starts and ends with a single quote, for example 'My name is Mozart'

我需要检查字符串是否以单引号开头和结尾，例如“我的名字是莫扎特”

What I have is this, which doesn't work

我有的是这个，这不起作用

if [[ $TEXT == '*' ]] ;

This does not work either

这也不起作用

if [[ $TEXT == /'*/' ]] ;

But if I change it to

但是如果我把它改成

if [[ $TEXT == a*a ]] ;

it works for a sentence like 'an amazing apa'. So I Believe it has to do with the single quote sign.

它适用于像“一个惊人的 apa”这样的句子。所以我相信它与单引号有关。

Any ideas on how I can solve it?

关于如何解决它的任何想法？

回答by Cyrus

With a regex:

使用正则表达式：

if [[ $TEXT =~ ^\'.*\'$ ]]

With globbing:

使用通配符：

if [[ $TEXT == \'*\' ]]

回答by Sulav Timsina

I am writing the complete bash script so you won't have any confusion:

我正在编写完整的 bash 脚本，所以您不会有任何困惑：

#! /bin/bash
text1="'helo there"
if [[ $text1 =~ ^\'.*\'$ ]]; then
        echo "text1 match"
else
        echo "text1 not match"

fi

text2="'hello babe'"
if [[ $text2 =~ ^\'.*\'$ ]]; then
        echo "text2 match"
else
        echo "text2 not match"
fi

Save the above script as matchCode.sh

将上面的脚本另存为 matchCode.sh

Now run it as: ./matchCode

现在运行它： ./matchCode

output:

输出：

text1 not match
text2 match

Ask if you have any confusion.

问你是否有任何困惑。

回答by mklement0

Cyrus' helpful answersolves your problem as posted.

赛勒斯的有用回答解决了您发布的问题。

However, I suspect you may be confused over quotes that are part of the shell syntaxvs. quotes that are actually part of the string:

但是，我怀疑您可能对作为 shell 语法一部分的引号与实际上是字符串一部分的引号感到困惑：

• In a POSIX-like shell such as Bash, 'My name is Mozart'is a single-quoted string whose content is the literal My name is Mozart- withoutthe enclosing '. That is, the enclosing 'characters are a syntactic elementsthat tell the shell that everything betweenthem is the literal contentsof the string.

• By contrast, to create a string whose contentis actually enclosed in '- i.e., has embedded'instances, you'd have to use something like: "'My name is Mozart'". Now it is the enclosing "instances that are the syntactic elements that bookend the string content.

  • Note, however, that using a "..."string (double quotes) makes the contents subject to string interpolation(expansion of embedded variable references, arithmetic and command substitutions; none in the case at hand, however), so it's important to know when to use '...'(literal strings) vs. "..."(interpolated strings).
  • Embedding 'instances in '...'strings is actually not supported at all in POSIX-like shells, but in Bash, Ksh, and Zsh there's another string type that allows you to do that: ANSI C-quoted strings, $'...', in which you can embed 'escaped as \': $'\'My name is Mozart\''
  • Another option is to use string concatenation: In POSIX-like shells, you can place substrings employing different quoting styles (including unquoted tokens) directlynext to one another in order to form a single string: "'"'My Name is Mozart'"'"would also give you a string with contents'My Name is Mozart'.
    POSIX-like shells also allow you to escape individual, unquoted characters(meaning: neither part of a single- nor a double-quoted string) with \; therefore, \''My name is Mozart'\'yields the same result.

• 在类似 POSIX 的 shell 中，例如 Bash，'My name is Mozart'是一个单引号字符串，其内容是文字My name is Mozart——没有封闭的'. 也就是说，封闭 '字符是一个句法元素，它告诉外壳它们之间的所有内容都是字符串的文字内容。

• 相比之下，创建一个字符串，其内容实际上是封闭的'-即已经嵌入的'情况下，你必须使用这样的："'My name is Mozart'"。现在它是包含"字符串内容的语法元素的封闭实例。

  • 但是请注意，使用"..."字符串（双引号）会使内容受到字符串插值的影响（嵌入变量引用的扩展、算术和命令替换；但是在手头的情况下没有），因此知道何时使用'...'(文字字符串）与"..."（内插字符串）。
  • '在'...'类似 POSIX 的 shell 中实际上根本不支持在字符串中嵌入实例，但是在 Bash、Ksh 和 Zsh 中，还有另一种字符串类型允许您这样做：ANSI C 引用的字符串, $'...'，您可以在其中嵌入'转义为\'：$'\'My name is Mozart\''
  • 另一种选择是使用字符串连接：在类似 POSIX 的 shell 中，您可以将采用不同引用样式（包括未加引号的标记）的子字符串直接放在一起，以形成单个字符串："'"'My Name is Mozart'"'"也会为您提供一个包含内容的字符串'My Name is Mozart'。
    类似 POSIX 的 shell 还允许您使用 ; 转义单个未加引号的字符（意思是：既不是单引号字符串的一部分，也不是双引号字符串的一部分）\。因此，\''My name is Mozart'\'产生相同的结果。

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The behavior of Bash's ==operator inside [[ ... ]](conditionals)may have added to the confusion:

Bash==操作符内部[[ ... ]]（条件）的行为可能增加了混乱：

If the RHS (right-hand side - the operand to the right of operator ==) is quoted, Bash treats it like a literal; only unquotedstrings (or variable references) are treated as (glob-like) patterns:

如果引用了 RHS（右侧 - operator 右侧的操作数==），Bash 会将其视为文字；只有未加引号的字符串（或变量引用）被视为（类似全局的）模式：

'*'matches literal*, whereas *(unquoted!) matches any sequence of characters, including none.

'*'匹配文字*，而*（未加引号！）匹配任何字符序列，包括无。

Thus:

因此：

• [[ $TEXT == '*' ]]would only ever match the single, literal character *.

• [[ $TEXT == /'*/' ]], because it mistakes /for the escape character - which in reality is \- would only match literal/*/(/'*/'is effectively a concatenation of unquoted /and single-quoted literal */).

• [[ $TEXT == a*a ]], due to using an unquotedRHS, is the only variant that actually performs pattern matching: any string that starts with aand ends with ais matched, including aa(because unquoted *represents any sequence of characters).

• [[ $TEXT == '*' ]]只会匹配单个文字字符*。

• [[ $TEXT == /'*/' ]]，因为它误/认为转义字符 - 实际上是\- 只会匹配文字/*/（/'*/'实际上是未引用/和单引号文字的串联*/）。

• [[ $TEXT == a*a ]]，由于使用了未加引号的RHS，它是实际执行模式匹配的唯一变体：任何以 开头a和结尾的字符串都a被匹配，包括aa（因为未加引号*表示任何字符序列）。

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To verify that Cyrus' commands do work with strings whose contentis enclosed in (embedded) single quotes, try these commands, which - on Bash, Ksh, and Zsh - should both output yes.

要验证 Cyrus 的命令是否适用于内容包含在（嵌入的）单引号中的字符串，请尝试这些命令，它们在 Bash、Ksh 和 Zsh 上都应该输出yes.

[[ "'ab'" == \'*\' ]] && echo yes  # pattern matching, indiv. escaped ' chars.

[[ "'ab'" =~ ^\'.*\'$ ]] && echo yes # regex operator =~