blocks|key|3171136|text|尝试foo[0...100]，任何范围都可以。范围也可以变为负数。它是Ruby的well+explained+in+the+documentation。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3171137|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-doc.org/core/classes/String.html^0|2|C|14|Z|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@$9|Q|A|R|1|S]]|E|$]]|$1|F|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

Try <code>foo[0...100]</code>, any range will do. Ranges can also go negative. It is <a href="http://ruby-doc.org/core/classes/String.html" rel="noreferrer">well explained in the documentation</a> of Ruby.

blocks|key|265685|text|使用[]-operator+(docs)：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|265686|foo[0,+100]++#+Get+100+characters+starting+at+position+0
foo[0..99]+++#+Get+all+characters+in+index+range+0+to+99+(inclusive!)
foo[0...100]+#+Get+all+characters+in+index+range+0+to+100+(exclusive!)|code-block|syntax|javascript|265687|Update+for+Ruby+2.7：Beginless+ranges现在在这里(截至2019-12-25)，可能是“返回数组的第一个xx”的标准答案：|265688|foo[...100]++#+Get+all+chars+from+the+beginning+up+until+the+100th+(exclusive)|265689|使用.slice方法(docs)：|265690|foo.slice(0,+100)++#+Get+100+characters+starting+at+position+0
foo.slice(0...100)+#+Behaves+the+same+as+operator+[]+|265691|为了完整性：|265692|foo[0]+++++++++#+Returns+the+indexed+character,+the+first+in+this+case
foo[-100,+100]+#+Get+100+characters+starting+at+position+-100
+++++++++++++++#+Negative+indices+are+counted+from+the+end+of+the+string/array
+++++++++++++++#+Caution:+Negative+indices+are+1-based,+the+last+element+is+-1
foo[-100..-1]++#+Get+the+last+100+characters+in+order
foo[-1..-100]++#+Get+the+last+100+characters+in+reverse+order
foo[-100...foo.length]+#+No+index+for+one+beyond+last+character|265693|Update+for+Ruby+2.6：Endless+ranges现在就在这里(截至2018-12-25)！|265694|foo[0..]++++++#+Get+all+chars+starting+at+the+first.+Identical+to+foo[0..-1]
foo[-100..]+++#+Get+the+last+100+characters|265695|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-doc.org/core-2.6/String.html#method-i-5B-5D|1|https://www.ruby-lang.org/en/news/2019/12/25/ruby-2-7-0-released/|2|https://blog.saeloun.com/2019/08/19/ruby-2-7-adds-beginless-range.html|3|http://ruby-doc.org/core-2.6/String.html#method-i-slice|4|https://www.ruby-lang.org/en/news/2018/12/25/ruby-2-6-0-released/|5|https://medium.com/square-corner-blog/rubys-new-infinite-range-syntax-0-97777cf06270^0|2|2|F|4|0|0|0|0|J|1|K|G|2|0|0|2|6|B|4|3|0|0|0|0|0|J|4|K|E|5|0|0^^$0|@$1|2|3|4|5|6|7|1I|8|@$9|1J|A|1K|B|C]]|D|@$9|1L|A|1M|1|1N]]|E|$]]|$1|F|3|G|5|H|7|1O|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1P|8|@]|D|@$9|1Q|A|1R|1|1S]|$9|1T|A|1U|1|1V]]|E|$]]|$1|M|3|N|5|H|7|1W|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1X|8|@$9|1Y|A|1Z|B|C]]|D|@$9|20|A|21|1|22]]|E|$]]|$1|Q|3|R|5|H|7|23|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|24|8|@]|D|@]|E|$]]|$1|U|3|V|5|H|7|25|8|@]|D|@]|E|$I|J]]|$1|W|3|X|5|6|7|26|8|@]|D|@$9|27|A|28|1|29]|$9|2A|A|2B|1|2C]]|E|$]]|$1|Y|3|Z|5|H|7|2D|8|@]|D|@]|E|$I|J]]|$1|10|3|-4|5|6|7|2E|8|@]|D|@]|E|$]]]|11|$12|$5|13|14|15|E|$16|17]]|18|$5|13|14|15|E|$16|19]]|1A|$5|13|14|15|E|$16|1B]]|1C|$5|13|14|15|E|$16|1D]]|1E|$5|13|14|15|E|$16|1F]]|1G|$5|13|14|15|E|$16|1H]]]]

Using the <code>[]</code>-operator (<a href="http://ruby-doc.org/core-2.6/String.html#method-i-5B-5D" rel="noreferrer">docs</a>):

<pre><code>foo[0, 100] # Get 100 characters starting at position 0
foo[0..99] # Get all characters in index range 0 to 99 (inclusive!)
foo[0...100] # Get all characters in index range 0 to 100 (exclusive!)
</code></pre>

<a href="https://www.ruby-lang.org/en/news/2019/12/25/ruby-2-7-0-released/" rel="noreferrer">Update for Ruby 2.7</a>: <a href="https://blog.saeloun.com/2019/08/19/ruby-2-7-adds-beginless-range.html" rel="noreferrer">Beginless ranges</a> are here now (as of 2019-12-25) and are probably the canonical answer for "return the first xx of an array":

<pre><code>foo[...100] # Get all chars from the beginning up until the 100th (exclusive)
</code></pre>

Using <code>.slice</code> method (<a href="http://ruby-doc.org/core-2.6/String.html#method-i-slice" rel="noreferrer">docs</a>):

<pre><code>foo.slice(0, 100) # Get 100 characters starting at position 0
foo.slice(0...100) # Behaves the same as operator [] 
</code></pre>

And for completeness:

<pre><code>foo[0] # Returns the indexed character, the first in this case
foo[-100, 100] # Get 100 characters starting at position -100
 # Negative indices are counted from the end of the string/array
 # Caution: Negative indices are 1-based, the last element is -1
foo[-100..-1] # Get the last 100 characters in order
foo[-1..-100] # Get the last 100 characters in reverse order
foo[-100...foo.length] # No index for one beyond last character
</code></pre>

<a href="https://www.ruby-lang.org/en/news/2018/12/25/ruby-2-6-0-released/" rel="noreferrer">Update for Ruby 2.6</a>: <a href="https://medium.com/square-corner-blog/rubys-new-infinite-range-syntax-0-97777cf06270" rel="noreferrer">Endless ranges</a> are here now (as of 2018-12-25)!

<pre><code>foo[0..] # Get all chars starting at the first. Identical to foo[0..-1]
foo[-100..] # Get the last 100 characters
</code></pre>

I am trying to find a function for select e.g. first 100 chars of the string. In PHP, there exists the substr<a href="http://www.php.net/manual/en/function.substr.php" rel="noreferrer"> function</a>

Does Ruby have some similar function?

Ruby - How to select some characters from string

我正在尝试寻找一个函数来选择字符串的前100个字符。在PHP中，存在substrRuby有类似的功能吗？

问Ruby -如何从字符串中选择一些字符
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