假设我有以下字符串： x="number 1;number 2;number 3" 。
通过${x%%";"*}成功访问第一个子字符串，访问最后一个子字符串是通过${x##*";"} ：
$ x="number 1;number 2;number 3" $ echo "front : ${x%%";"*}" #front-most-part number 1 $ echo "back : ${x##*";"}" #back-most-part number 3 $我如何访问中间部分:(例如， number 2 ）？ 如果我有（很多......）更多零件然后只有三个，有更好的方法吗？ 换句话说：是否存在访问字符串yyy子字符串n的通用方法，由字符串xxx分隔，其中xxx是一个任意字符串/分隔符？
我已阅读如何在Bash中的分隔符上拆分字符串？ ，但我特别不想迭代字符串，而是直接访问给定的子字符串。
这特别不要求或分成数组，而是分成子字符串。
Let's assume I have the following string: x="number 1;number 2;number 3".
Access to the first substring is successfull via ${x%%";"*}, access to the last substring is via ${x##*";"}:
$ x="number 1;number 2;number 3" $ echo "front : ${x%%";"*}" #front-most-part number 1 $ echo "back : ${x##*";"}" #back-most-part number 3 $How do I access the middle part: (eg. number 2)? Is there a better way to do this if I have (many...) more parts then just three? In other words: Is there a generic way of accessing substring No. n of string yyy, delimited by string xxx where xxx is an arbitraty string/delimiter?
I have read How do I split a string on a delimiter in Bash?, but I specifically do not want to iterate over the string but rather directly access a given substring.
This specifically does not ask or a split into arrays, but into sub-strings.
最满意答案
使用固定索引：
x="number 1;number 2;number 3" # Split input into fields by ';' and read the 2nd field into $f2 # Note the need for the *2nd* `unused`, otherwise f2 would # receive the 2nd field *plus the remainder of the line*. IFS=';' read -r unused f2 unused <<<"$x" echo "$f2"通常，使用数组：
x="number 1;number 2;number 3" # Split input int fields by ';' and read all resulting fields # into an *array* (-a). IFS=';' read -r -a fields <<<"$x" # Access the desired field. ndx=1 echo "${fields[ndx]}"制约因素 ：
使用IFS ，指定I nternal Field S eparator字符的特殊变量， 总是意味着：
只有单个文字字符可以充当字段分隔符。
但是，您可以指定多个字符，在这种情况下， 任何字符都将被视为分隔符。默认的分隔符是$' \t\n' - 即空格，制表符和换行符，它们的运行 （多个连续的实例）始终被视为单个分隔符; 例如， 'a b'有2个字段 - 多个空格计为单个分隔符。
相比之下， 对于任何其他字符 ，运行中的字符被单独考虑，因此分开空字段; 例如， 'a;;b'有3个字段 - 每个字段; 是它自己的分隔符，所以之间有一个空字段;; 。
read -r -a ... <<<...技术通常效果很好，只要 ：
输入是单行的 你不关心被遗弃的尾随空场如果您需要一个解决上述问题的完全通用，强大的解决方案 ，请使用以下变体，这在@gniourf_gniourf中的解释如下 ：
sep=';' IFS="$sep" read -r -d '' -a fields < <(printf "%s${sep}\0" "$x")注意需要使用-d ''一次读取多行输入，并且需要使用另一个分隔符实例终止输入以保留尾随的空字段; 需要尾随\0以确保read的退出代码为0 。
With a fixed index:
x="number 1;number 2;number 3" # Split input into fields by ';' and read the 2nd field into $f2 # Note the need for the *2nd* `unused`, otherwise f2 would # receive the 2nd field *plus the remainder of the line*. IFS=';' read -r unused f2 unused <<<"$x" echo "$f2"Generically, using an array:
x="number 1;number 2;number 3" # Split input int fields by ';' and read all resulting fields # into an *array* (-a). IFS=';' read -r -a fields <<<"$x" # Access the desired field. ndx=1 echo "${fields[ndx]}"Constraints:
Using IFS, the special variable specifying the Internal Field Separator characters, invariably means:
Only single, literal characters can act as field separators.
However, you can specify multiple characters, in which case any of them is treated as a separator.The default separator characters are $' \t\n' - i.e., space, tab, and newline, and runs of them (multiple contiguious instances) are always considered a single separator; e.g., 'a b' has 2 fields - the multiple space count as a single separator.
By contrast, with any other character, characters in a run are considered separately, and thus separate empty fields; e.g., 'a;;b' has 3 fields - each ; is its own separator, so there's an empty field between ;;.
The read -r -a ... <<<... technique generally works well, as long as:
the input is single-line you're not concerned about a trailing empty field getting discardedIf you need a fully generic, robust solution that addresses the issues above, use the following variation, which is explained in @gniourf_gniourf answer here:
sep=';' IFS="$sep" read -r -d '' -a fields < <(printf "%s${sep}\0" "$x")Note the need to use -d '' to read multi-line input all at once, and the need to terminate the input with another separator instance to preserve a trailing empty field; the trailing \0 is needed to ensure that read's exit code is 0.
更多推荐
发布评论