什么 linuxshell 命令返回字符串的一部分？

我想找到一个可以返回字符串一部分的 linux 命令。在大多数编程语言中，它是 substr()函数。Bash 是否有任何可用于此目的的命令。我想做这样的事。 指纹 cde。

接下来的类似问题:

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From the bash manpage:

${parameter:offset}
${parameter:offset:length}
Substring  Expansion.   Expands  to  up  to length characters of
parameter starting at the character  specified  by  offset.
[...]

Or, if you are not sure of having bash, consider using cut.

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In bash you can try this:

stringZ=abcABC123ABCabc
#       0123456789.....
#       0-based indexing.


echo ${stringZ:0:2} # prints ab

More samples in The Linux Documentation Project

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${string:position:length}
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最佳答案

If you are looking for a shell utility to do something like that, you can use the cut command.

To take your example, try:

echo "abcdefg" | cut -c3-5

which yields

cde

Where -cN-M tells the cut command to return columns N to M, inclusive.

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expr(1) has a substr subcommand:

expr substr <string> <start-index> <length>

This may be useful if you don't have bash (perhaps embedded Linux) and you don't want the extra "echo" process you need to use cut(1).

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In "pure" bash you have many tools for (sub)string manipulation, mainly, but not exclusively in parameter expansion :

${parameter//substring/replacement}
${parameter##remove_matching_prefix}
${parameter%%remove_matching_suffix}

Indexed substring expansion (special behaviours with negative offsets, and, in newer Bashes, negative lengths):

${parameter:offset}
${parameter:offset:length}
${parameter:offset:length}

And of course, the much useful expansions that operate on whether the parameter is null:

${parameter:+use this if param is NOT null}
${parameter:-use this if param is null}
${parameter:=use this and assign to param if param is null}
${parameter:?show this error if param is null}

They have more tweakable behaviours than those listed, and as I said, there are other ways to manipulate strings (a common one being $(command substitution) combined with sed or any other external filter). But, they are so easily found by typing man bash that I don't feel it merits to further extend this post.


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