在 Bash 正则表达式中，`^` 和 `$` 是指行，还是指整个字符串？
In Bash regular expressions do `^` and `$` refer to lines, or to the entire string?
在The Linux Documentation Project (I didn't find details about the regex metacharacters in the Bash manual)中，元字符^和$被定义为匹配行：
^: Matches the empty string at the beginning of a line [...]
$: Matches the empty string at the end of a line
然而，当我尝试时，这是不正确的：
$ string="a
> b
> c"
$ [[ $string =~ ^a ]] && echo BOS match
BOS match
$ [[ $string =~ ^b ]] && echo BOL match
# nothing
是手册真的错了，还是我遗漏了什么？
^ 匹配整个输入字符串的开头，$ 匹配 POSIX 正则表达式中整个输入字符串的结尾（Bash 使用 POSIX ERE）。您 link 提到的文档中提到行是因为大多数文本处理工具，如 sed、grep 或 awk 默认情况下逐行读取输入，并且字符串与行一致在大多数情况下。
9.3.8 BRE Expression Anchoring
A BRE can be limited to matching strings that begin or end a line; this is called "anchoring". The circumflex and dollar sign special characters shall be considered BRE anchors in the following contexts:
A circumflex ( '^' ) shall be an anchor when used as the first character of an entire BRE. The implementation may treat the circumflex as an anchor when used as the first character of a subexpression. The circumflex shall anchor the expression (or optionally subexpression) to the beginning of a string; only sequences starting at the first character of a string shall be matched by the BRE. For example, the BRE "^ab" matches "ab" in the string "abcdef", but fails to match in the string "cdefab". The BRE "(^ab)" may match the former string. A portable BRE shall escape a leading circumflex in a subexpression to match a literal circumflex.
A dollar sign ( '$' ) shall be an anchor when used as the last character of an entire BRE. The implementation may treat a dollar sign as an anchor when used as the last character of a subexpression. The dollar sign shall anchor the expression (or optionally subexpression) to the end of the string being matched; the dollar sign can be said to match the end-of-string following the last character.
A BRE anchored by both '^' and '$' shall match only an entire string. For example, the BRE "^abcdef$" matches strings consisting only of "abcdef".
在The Linux Documentation Project (I didn't find details about the regex metacharacters in the Bash manual)中，元字符^和$被定义为匹配行：
^: Matches the empty string at the beginning of a line [...]
$: Matches the empty string at the end of a line
然而，当我尝试时，这是不正确的：
$ string="a
> b
> c"
$ [[ $string =~ ^a ]] && echo BOS match
BOS match
$ [[ $string =~ ^b ]] && echo BOL match
# nothing
是手册真的错了，还是我遗漏了什么？
^ 匹配整个输入字符串的开头，$ 匹配 POSIX 正则表达式中整个输入字符串的结尾（Bash 使用 POSIX ERE）。您 link 提到的文档中提到行是因为大多数文本处理工具，如 sed、grep 或 awk 默认情况下逐行读取输入，并且字符串与行一致在大多数情况下。
9.3.8 BRE Expression Anchoring
A BRE can be limited to matching strings that begin or end a line; this is called "anchoring". The circumflex and dollar sign special characters shall be considered BRE anchors in the following contexts:
A circumflex (
'^') shall be an anchor when used as the first character of an entire BRE. The implementation may treat the circumflex as an anchor when used as the first character of a subexpression. The circumflex shall anchor the expression (or optionally subexpression) to the beginning of a string; only sequences starting at the first character of a string shall be matched by the BRE. For example, the BRE "^ab" matches "ab" in the string "abcdef", but fails to match in the string "cdefab". The BRE "(^ab)" may match the former string. A portable BRE shall escape a leading circumflex in a subexpression to match a literal circumflex.A dollar sign (
'$') shall be an anchor when used as the last character of an entire BRE. The implementation may treat a dollar sign as an anchor when used as the last character of a subexpression. The dollar sign shall anchor the expression (or optionally subexpression) to the end of the string being matched; the dollar sign can be said to match the end-of-string following the last character.A BRE anchored by both
'^'and'$'shall match only an entire string. For example, the BRE"^abcdef$"matches strings consisting only of"abcdef".