blocks|key|1165118|text|grep将通过查看argv[0]来检查其调用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1165119|下面是一个简短的演示程序：|1165120|>+cat+someprogram.cpp+
#include+<iostream>

int+main(int+argc,+char*+argv[])
{
++++std::cout+<<+"Shall+behave+as+"+<<+argv[0]+<<+"."+<<+std::endl;
}|code-block|syntax|javascript|1165121|内部版本：|1165122|>+make+someprogram
g%2B%2B+someprogram.cpp+++-o+someprogram|1165123|创建符号链接：|1165124|>+ln+-s+someprogram+some_other_program|1165125|运行一次：|1165126|>+./someprogram
Shall+behave+as+./someprogram.|1165127|运行两次：|1165128|>+./some_other_program+
Shall+behave+as+./some_other_program.|1165129|Gnu+grep是free和开源软件，因此您可以自由地检查the+source。|1165130|entityMap|0|LINK|mutability|MUTABLE|url|http://www.gnu.org/software/grep/|1|http://www.gnu.org/philosophy/open-source-misses-the-point.html|2|http://git.savannah.gnu.org/cgit/grep.git/tree/^0|0|4|9|7|0|0|0|0|0|0|0|0|0|0|0|4|4|0|8|0|9|4|1|T|A|2|0^^$0|@$1|2|3|4|5|6|7|1G|8|@$9|1H|A|1I|B|C]|$9|1J|A|1K|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1L|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1M|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1N|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1O|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1P|8|@]|D|@]|E|$]]|$1|S|3|T|5|J|7|1Q|8|@]|D|@]|E|$K|L]]|$1|U|3|V|5|6|7|1R|8|@]|D|@]|E|$]]|$1|W|3|X|5|J|7|1S|8|@]|D|@]|E|$K|L]]|$1|Y|3|Z|5|6|7|1T|8|@]|D|@]|E|$]]|$1|10|3|11|5|J|7|1U|8|@]|D|@]|E|$K|L]]|$1|12|3|13|5|6|7|1V|8|@$9|1W|A|1X|B|C]]|D|@$9|1Y|A|1Z|1|20]|$9|21|A|22|1|23]|$9|24|A|25|1|26]]|E|$]]|$1|14|3|-4|5|6|7|27|8|@]|D|@]|E|$]]]|15|$16|$5|17|18|19|E|$1A|1B]]|1C|$5|17|18|19|E|$1A|1D]]|1E|$5|17|18|19|E|$1A|1F]]]]

<code>grep</code> will check its invocation by looking at <code>argv[0]</code>.

Here's a short program to demonstrate:

<pre><code>&gt; cat someprogram.cpp 
#include &lt;iostream&gt;

int main(int argc, char* argv[])
{
 std::cout &lt;&lt; "Shall behave as " &lt;&lt; argv[0] &lt;&lt; "." &lt;&lt; std::endl;
}
</code></pre>

Build:

<pre><code>&gt; make someprogram
g++ someprogram.cpp -o someprogram
</code></pre>

Make a symbolic link:

<pre><code>&gt; ln -s someprogram some_other_program
</code></pre>

Run one:

<pre><code>&gt; ./someprogram
Shall behave as ./someprogram.
</code></pre>

Run two:

<pre><code>&gt; ./some_other_program 
Shall behave as ./some_other_program.
</code></pre>

<a href="http://www.gnu.org/software/grep/" rel="nofollow">Gnu <code>grep</code></a> is <a href="http://www.gnu.org/philosophy/open-source-misses-the-point.html" rel="nofollow">free</a> and open source software, so you are free to examine <a href="http://git.savannah.gnu.org/cgit/grep.git/tree/" rel="nofollow">the source</a>.

blocks|key|5203821|text|因为可执行文件检查argv[0]的值并相应地调整其行为。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5203822|entityMap^0|9|7|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

Because the executable checks the value of <code>argv[0]</code> and adjusts its behavior accordingly.

blocks|key|5203878|text|因为POSIX认为egrep等同于grep+-E而不是普通的grep，而fgrep等同于grep+-F而不是普通的grep。如果希望grep的行为与egrep相同，请使用grep+-E，依此类推。还有大约40年的先例问题。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5203879|entityMap|0|LINK|mutability|MUTABLE|url|http://pubs.opengroup.org/onlinepubs/9699919799/utilities/grep.html^0|9|5|H|7|U|4|10|5|18|7|1L|4|1U|4|22|5|2D|7|H|7|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]|$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]]|D|@$9|16|A|17|1|18]]|E|$]]|$1|F|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

Because POSIX says that <code>egrep</code> is equivalent to <a href="http://pubs.opengroup.org/onlinepubs/9699919799/utilities/grep.html" rel="nofollow"><code>grep -E</code></a> and not plain <code>grep</code>, and <code>fgrep</code> is equivalent to <code>grep -F</code> and not plain <code>grep</code>. If you want <code>grep</code> to behave the same as <code>egrep</code>, use <code>grep -E</code>, and so on. There is also the issue of about 40 years of precedent.

blocks|key|1165204|text|除了正则表达式引擎之外，功能是相同的；共享代码是有意义的，可以通过创建库(如今更常见的方法)，也可以通过使用单个二进制文件(检查其名称(argv[0])来确定请求的行为)。(当然，第三种可能是使用单个名称并使用选项来选择不同的行为。这就是像git和tar这样的命令所做的事情；一个命令就是“界面”，但是通过指定不同的操作，您会得到截然不同的行为。)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1165205|之所以有不同的命令，是一个长期的遗留问题，可以追溯到Unix的早期。普通老式grep是正则表达式最早的实现之一，随着开发人员对这一特定问题领域的理解的提高，具有新功能的新工具不断发展。出于向后兼容性的原因，这些新功能不能简单地集成到grep中(这将改变其行为)，因此新命令具有新的名称。到POSIX开始标准化时，grep、egrep和fgrep之间的分工已经牢固确立，尽管事后看来，您可能会认为它们中至少有一个是多余的。|1165206|entityMap^0|1W|7|3C|3|3G|3|0|12|4|38|4|4C|4|4H|5|4N|5|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|I|$]]

The functionality is identical apart from the regex engine; it makes sense to share the code, either by creating a library (a more common approach these days) or by using a single binary which examines its name (<code>argv[0]</code>) to determine which behavior is requested. (A third possibility is to have a single name and use options to select different behaviors, of course. This is what commands like <code>git</code> and <code>tar</code> do; a single command is the "interface" but you get vastly different behaviors by specifying different actions.)

The reason there are distinct commands is a long legacy, going back to the early days of Unix. Plain old <code>grep</code> was one of the earliest implementations of regular expressions, and as the developers' understanding of this particular problem domain improved, new tools with new capabilities evolved. For reasons of backwards compatibility, these new features could not simply be integrated to <code>grep</code> (this would have changed its behavior) so the new commands had new names. By the time POSIX got around to standardizing things, the division of labor between <code>grep</code>, <code>egrep</code> and <code>fgrep</code> was firmly established, although in hindsight, you could argue that at least one of them is redundant.

<pre><code>$ ls -l /bin/*grep
lrwxrwxrwx 1 root root 4 2010-06-09 02:56 /bin/egrep -&gt; grep
lrwxrwxrwx 1 root root 4 2010-06-09 02:56 /bin/fgrep -&gt; grep
-rwxr-xr-x 1 root root 85060 2007-01-23 02:00 /bin/grep

$ echo 'hello' | grep -q 'l{2}' &amp;&amp; echo YES || echo NO
NO

$ echo 'hello' | egrep -q 'l{2}' &amp;&amp; echo YES || echo NO
YES
</code></pre>

In my system, <code>egrep</code> is a symbolic link to <code>grep</code>, but they behave differently. Why?

Why do egrep and grep behave differently although they are the same binary?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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$ ls -l /bin/*greplrwxrwxrwx 1 root root     4 2010-06-09 02:56 /bin/egrep -> greplrwxrwxrwx 1 root root     4 2010-06-09 02:56 /bin/fgrep -> grep-rwxr-xr-x 1 root root 85060 2007-01-23 02:00 /bin/gre

问为什么egrep和grep的行为不同，尽管它们是相同的二进制文件？
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问为什么egrep和grep的行为不同，尽管它们是相同的二进制文件？EN

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问为什么egrep和grep的行为不同，尽管它们是相同的二进制文件？
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