perl的shasum VS庆典shasum [英] perl shasum vs bash shasum

问题描述

以下bash和Perl脚本神秘给出不同的结果。为什么呢？

The following bash and Perl scripts mysteriously give different results. Why?

#!/bin/bash                                                                       
hash=`echo -n 'abcd' | /usr/bin/shasum -a 256`;
echo $hash;

#!/usr/bin/perl                                                                   
$hash = `echo -n 'abcd' | /usr/bin/shasum -a 256`;
print "$hash";

在bash脚本：

The bash script:

$ ./tst.sh
88d4266fd4e6338d13b845fcf289579d209c897823b9217da3e161936f031589 -

的Perl脚本：

The Perl script:

$ ./tst.pl
61799467ee1ab1f607764ab36c061f09cfac2f9c554e13f4c7442e66cbab9403  -

到底？

推荐答案

摘要：在你的Perl脚本， -n 被当作参数传递给输出包括回声，而不是一个标志燮preSS的换行符。 （尝试

Summary: In your Perl script, -n is being treated as an argument to include in the output of echo, not a flag to suppress the newline. ( Try

$hash = `echo -n 'abcd'`;

确认）。使用的printf 代替。

Perl使用 / bin / sh的执行中回抽动code。即使 / bin / sh的是庆典的链接，当通过像调用它会表现不同。在POSIX模式，

Perl uses /bin/sh to execute code in back tics. Even if /bin/sh is a link to bash, it will behave differently when invoked via that like. In POSIX mode,

echo -n 'abcd'

将输出

-n abcd

也就是 -n 选项不能被识别为一个标志燮preSS一个换行符，而是被当作常规参数进行打印。替换回声-n 与的printf 中的每个脚本，您应该从每个脚本相同SHA散列。

that is, the -n option is not recognized as a flag to suppress a newline, but is treated as a regular argument to print. Replace echo -n with printf in each script, and you should get the same SHA hash from each script.

（更新：庆典 3.2时为 SH 调用，显示此行为较新版本的庆典似乎继续治疗 -n 当为 SH 。）

(UPDATE: bash 3.2, when invoked as sh, displays this behavior. Newer versions of bash seem to continue treating -n as a flag when invoked as sh.)

更妙的是，不要掏出做的事情，你可以在Perl做的。

Even better, don't shell out to do things you can do in Perl.

use Digest::SHA;

$hash = Digest::SHA::sha256('abcd');

---

有关好奇，这里是什么POSIX规范有什么看法<$ C $ C>回声。我不知道做XSI一致性的东西; 庆典 回声要求 -e 选项，可将逃生字符特别，但几乎每个壳MDASH; 除了的旧版本庆典，然后只有在特殊情况下＆MDASH;治疗 -n 作为一个标志，而不是一个字符串。哦。

---

For the curious, here's what the POSIX spec has to say about echo. I'm not sure what to make of XSI conformance; bash echo requires the -e option to treat the escape characters specially, but nearly every shell—except old versions of bash, and then only under special circumstances—treats -n as a flag, not a string. Oh well.

The following operands shall be supported:

string
A string to be written to standard output. If the first operand is -n, or
if any of the operands contain a <backslash> character, the results are
implementation-defined.

On XSI-conformant systems, if the first operand is -n, it shall be treated
as a string, not an option. The following character sequences shall be
recognized on XSI-conformant systems within any of the arguments:

\a
Write an <alert>.
\b
Write a <backspace>.
\c
Suppress the <newline> that otherwise follows the final argument in the output. All characters following the '\c' in the arguments shall be ignored.
\f
Write a <form-feed>.
\n
Write a <newline>.
\r
Write a <carriage-return>.
\t
Write a <tab>.
\v
Write a <vertical-tab>.
\\
Write a <backslash> character.
\0num
Write an 8-bit value that is the zero, one, two, or three-digit octal number num.

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