blocks|key|600948|text|如果使用文件名作为第一个参数$1调用脚本，则以下解决方案将从文件中读取，否则将从标准输入中读取。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|600949|while+read+line
do
++echo+"$line"
done+<+"${1:-/dev/stdin}"|code-block|syntax|javascript|600950|如果定义了替换${1:-...}，则它采用$1。否则，将使用自己进程的标准输入的文件名。|600951|entityMap^0|E|2|0|0|7|9|L|2|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

The following solution reads from a file if the script is called with a file name as the first parameter <code>$1</code> and otherwise from standard input.
<pre><code>while read line
do
 echo &quot;$line&quot;
done &lt; &quot;${1:-/dev/stdin}&quot;
</code></pre>
The substitution <code>${1:-...}</code> takes <code>$1</code> if defined. Otherwise, the file name of the standard input of the own process is used.

blocks|key|816437|text|也许最简单的解决方案是使用合并重定向操作符来重定向标准输入：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|816438|#!/bin/bash
less+<&0|code-block|syntax|javascript|816439|标准输入是文件描述符零。上面的代码将通过管道传输到bash脚本的输入发送到less's标准输入。|offset|length|816440|Read+more+about+file+descriptor+redirection。|816441|entityMap|0|LINK|mutability|MUTABLE|url|https://en.wikipedia.org/wiki/Less_(Unix)|1|https://developer.apple.com/library/mac/#documentation/opensource/Conceptual/ShellScripting/ShellInputandOutput/ShellInputandOutput.html#//apple_ref/doc/uid/TP40004268-CH3-SW9^0|0|0|11|6|0|0|0|17|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@]|9|@$I|Z|J|10|1|11]]|A|$]]|$1|K|3|L|5|6|7|12|8|@]|9|@$I|13|J|14|1|15]]|A|$]]|$1|M|3|-4|5|6|7|16|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]|U|$5|P|Q|R|A|$S|V]]]]

Perhaps the simplest solution is to redirect standard input with a merging redirect operator:
<pre><code>#!/bin/bash
less &lt;&amp;0
</code></pre>
Standard input is file descriptor zero. The above sends the input piped to your bash script into <a href="https://en.wikipedia.org/wiki/Less_(Unix)" rel="noreferrer">less's</a> standard input.
<a href="https://developer.apple.com/library/mac/#documentation/opensource/Conceptual/ShellScripting/ShellInputandOutput/ShellInputandOutput.html#//apple_ref/doc/uid/TP40004268-CH3-SW9" rel="noreferrer">Read more about file descriptor redirection</a>.

blocks|key|816524|text|我认为这是最简单的方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|816525|$+cat+reader.sh
#!/bin/bash
while+read+line;+do
++echo+"reading:+${line}"
done+<+/dev/stdin|code-block|syntax|javascript|816526|--|816527|$+cat+writer.sh
#!/bin/bash
for+i+in+{0..5};+do
++echo+"line+${i}"
done|816528|816529|$+./writer.sh+%7C+./reader.sh
reading:+line+0
reading:+line+1
reading:+line+2
reading:+line+3
reading:+line+4
reading:+line+5|816530|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Q|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|R|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|K|3|H|5|6|7|T|8|@]|9|@]|A|$]]|$1|L|3|M|5|D|7|U|8|@]|9|@]|A|$E|F]]|$1|N|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|O|$]]

I think this is the straightforward way:
<pre><code>$ cat reader.sh
#!/bin/bash
while read line; do
 echo &quot;reading: ${line}&quot;
done &lt; /dev/stdin
</code></pre>
--
<pre><code>$ cat writer.sh
#!/bin/bash
for i in {0..5}; do
 echo &quot;line ${i}&quot;
done
</code></pre>
--
<pre><code>$ ./writer.sh | ./reader.sh
reading: line 0
reading: line 1
reading: line 2
reading: line 3
reading: line 4
reading: line 5
</code></pre>

blocks|key|816369|text|每当IFS中断输入流时，echo解决方案都会添加新的行。@fgm's+answer可以稍微修改一下：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|816370|cat+"${1:-/dev/stdin}"+>+"${2:-/dev/stdout}"|code-block|syntax|javascript|816371|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/7045517/55075^0|2|3|C|4|S|D|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

The <code>echo</code> solution adds new lines whenever <code>IFS</code> breaks the input stream. <a href="https://stackoverflow.com/a/7045517/55075">@fgm's answer</a> can be modified a bit:

<pre><code>cat "${1:-/dev/stdin}" &gt; "${2:-/dev/stdout}"
</code></pre>

blocks|key|601237|text|Perl的行为和OP中给出的代码可以不带参数，也可以有多个参数，如果参数是一个连字符-，则将其理解为stdin。此外，始终可以使用$ARGV作为文件名。到目前为止，没有一个答案真正模仿了Perl在这些方面的行为。这是一种纯粹的Bash可能性。诀窍是适当地使用exec。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|601238|#!/bin/bash

(($#))+%7C%7C+set+--+-
while+(($#));+do
+++{+[[+$1+=+-+]]+%7C%7C+exec+<+"$1";+}+&&
+++while+read+-r;+do
++++++printf+'%25s\n'+"$REPLY"
+++done
+++shift
done|code-block|syntax|javascript|601239|文件名在$1中可用。|601240|如果没有给定参数，我们就人为地将-设置为第一个位置参数。然后我们循环参数。如果参数不是-，我们就用exec重定向来自filename的标准输入。如果重定向成功，我们将使用while循环进行循环。我使用的是标准的REPLY变量，在这种情况下，您不需要重置IFS。如果你想要另一个名字，你必须像这样重置IFS+(当然，除非你不想这样做并且知道你在做什么)：|601241|while+IFS=+read+-r+line;+do
++++printf+'%25s\n'+"$line"
done|601242|entityMap^0|16|1|1T|5|3L|4|0|0|4|2|0|G|1|17|1|1D|4|2D|5|2X|5|3I|3|45|3|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|O|3|P|5|H|7|1I|8|@]|D|@]|E|$I|J]]|$1|Q|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|R|$]]

Perl's behavior, with the code given in the OP can take none or several arguments, and if an argument is a single hyphen <code>-</code> this is understood as stdin. Moreover, it's always possible to have the filename with <code>$ARGV</code>.
None of the answers given so far really mimic Perl's behavior in these respects. Here's a pure Bash possibility. The trick is to use <code>exec</code> appropriately.

<pre><code>#!/bin/bash

(($#)) || set -- -
while (($#)); do
 { [[ $1 = - ]] || exec &lt; "$1"; } &amp;&amp;
 while read -r; do
 printf '%s\n' "$REPLY"
 done
 shift
done
</code></pre>

Filename's available in <code>$1</code>.

If no arguments are given, we artificially set <code>-</code> as the first positional parameter. We then loop on the parameters. If a parameter is not <code>-</code>, we redirect standard input from filename with <code>exec</code>. If this redirection succeeds we loop with a <code>while</code> loop. I'm using the standard <code>REPLY</code> variable, and in this case you don't need to reset <code>IFS</code>. If you want another name, you must reset <code>IFS</code> like so (unless, of course, you don't want that and know what you're doing):

<pre><code>while IFS= read -r line; do
 printf '%s\n' "$line"
done
</code></pre>

blocks|key|816228|text|请尝试以下代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|816229|while+IFS=+read+-r+line;+do
++++echo+"$line"
done+<+file|code-block|syntax|javascript|816230|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Please try the following code:

<pre><code>while IFS= read -r line; do
 echo "$line"
done &lt; file
</code></pre>

blocks|key|816262|text|更准确的说...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|816263|while+IFS=+read+-r+line+;+do
++++printf+"%25s\n"+"$line"
done+<+file|code-block|syntax|javascript|816264|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

More accurately...

<pre><code>while IFS= read -r line ; do
 printf "%s\n" "$line"
done &lt; file
</code></pre>

blocks|key|601490|text|#!/usr/bin/bash

if+[+-p+/dev/stdin+];+then
+++++++#for+FILE+in+"$@"+/dev/stdin
++++for+FILE+in+/dev/stdin
++++do
++++++++while+IFS=+read+-r+LINE
++++++++do
++++++++++++echo+"$@"+"$LINE"+++#print+line+argument+and+stdin
++++++++done+<+"$FILE"
++++done
else
++++printf+"[+-p+/dev/stdin+]+is+false\n"
+++++#dosomething
fi|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|601491|运行：|unstyled|601492|echo+var+var2+%7C+bash+std.sh|601493|结果：|601494|var+var2|601495|601496|bash+std.sh+<+<(cat+/etc/passwd)|601497|601498|root:x:0:0::/root:/usr/bin/bash
bin:x:1:1::/:/usr/bin/nologin
daemon:x:2:2::/:/usr/bin/nologin
mail:x:8:12::/var/spool/mail:/usr/bin/nologin|601499|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|V|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|X|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$B|C]]|$1|M|3|E|5|F|7|Z|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|10|8|@]|9|@]|A|$B|C]]|$1|P|3|J|5|F|7|11|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|12|8|@]|9|@]|A|$B|C]]|$1|S|3|-4|5|F|7|13|8|@]|9|@]|A|$]]]|T|$]]

<pre><code>#!/usr/bin/bash

if [ -p /dev/stdin ]; then
 #for FILE in &quot;$@&quot; /dev/stdin
 for FILE in /dev/stdin
 do
 while IFS= read -r LINE
 do
 echo &quot;$@&quot; &quot;$LINE&quot; #print line argument and stdin
 done &lt; &quot;$FILE&quot;
 done
else
 printf &quot;[ -p /dev/stdin ] is false\n&quot;
 #dosomething
fi
</code></pre>
Running:
<pre><code>echo var var2 | bash std.sh
</code></pre>
Result:
<pre><code>var var2
</code></pre>
Running:
<pre><code>bash std.sh &lt; &lt;(cat /etc/passwd)
</code></pre>
Result:
<pre><code>root:x:0:0::/root:/usr/bin/bash
bin:x:1:1::/:/usr/bin/nologin
daemon:x:2:2::/:/usr/bin/nologin
mail:x:8:12::/var/spool/mail:/usr/bin/nologin
</code></pre>

blocks|key|816757|text|代码${1:-/dev/stdin}只会理解第一个参数，所以您可以使用下面的代码：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|816758|ARGS='$*'
if+[+-z+"$*"+];+then
++ARGS='-'
fi
eval+"cat+--+$ARGS"+%7C+while+read+line
do
+++echo+"$line"
done|code-block|syntax|javascript|816759|entityMap^0|2|G|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

The code <code>${1:-/dev/stdin}</code> will just understand the first argument, so you can use this:
<pre><code>ARGS='$*'
if [ -z &quot;$*&quot; ]; then
 ARGS='-'
fi
eval &quot;cat -- $ARGS&quot; | while read line
do
 echo &quot;$line&quot;
done
</code></pre>

blocks|key|816820|text|我不认为这些答案中的任何一个是可以接受的。具体地说，接受的答案只处理第一个命令行参数，而忽略其余参数。它试图模拟的Perl程序处理所有命令行参数。所以被接受的答案甚至不能回答这个问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|816821|其他答案使用Bash扩展，添加不必要的'cat‘命令，仅适用于将输入回显到输出的简单情况，或者只是不必要的复杂。|816822|然而，我必须给他们一些信任，因为他们给了我一些想法。以下是完整的答案：|816823|#!/bin/sh

if+[+$#+=+0+]
then
++++++++DEFAULT_INPUT_FILE=/dev/stdin
else
++++++++DEFAULT_INPUT_FILE=
fi

#+Iterates+over+all+parameters+or+/dev/stdin
for+FILE+in+"$@"+$DEFAULT_INPUT_FILE
do
++++++++while+IFS=+read+-r+LINE
++++++++do
++++++++++++++++#+Do+whatever+you+want+with+LINE+here.
++++++++++++++++echo+$LINE
++++++++done+<+"$FILE"
done|code-block|syntax|javascript|816824|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|O|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|P|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I don't find any of these answers acceptable. In particular, the accepted answer only handles the first command line parameter and ignores the rest. The Perl program that it is trying to emulate handles all the command line parameters. So the accepted answer doesn't even answer the question.
Other answers use Bash extensions, add unnecessary 'cat' commands, only work for the simple case of echoing input to output, or are just unnecessarily complicated.
However, I have to give them some credit, because they gave me some ideas. Here is the complete answer:
<pre><code>#!/bin/sh

if [ $# = 0 ]
then
 DEFAULT_INPUT_FILE=/dev/stdin
else
 DEFAULT_INPUT_FILE=
fi

# Iterates over all parameters or /dev/stdin
for FILE in &quot;$@&quot; $DEFAULT_INPUT_FILE
do
 while IFS= read -r LINE
 do
 # Do whatever you want with LINE here.
 echo $LINE
 done &lt; &quot;$FILE&quot;
done
</code></pre>

blocks|key|816696|text|以下代码适用于标准sh+(在Debian上使用Dash测试)，可读性很好，但这是一个品味问题：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|816697|if+[+-n+"$1"+];+then
++++cat+"$1"
else
++++cat
fi+%7C+commands_and_transformations|code-block|syntax|javascript|816698|详细信息:如果第一个参数非空，则cat该文件，否则为cat标准输入。然后由commands_and_transformations处理整个if语句的输出。|816699|entityMap|0|LINK|mutability|MUTABLE|url|https://en.wikipedia.org/wiki/Almquist_shell#dash:_Ubuntu,_Debian_and_POSIX_compliance_of_Linux_distributions^0|9|2|N|4|0|0|0|G|3|Q|3|11|S|1X|2|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|11|8|@$9|12|A|13|B|C]|$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

The following works with standard <code>sh</code> (tested with <a href="https://en.wikipedia.org/wiki/Almquist_shell#dash:_Ubuntu,_Debian_and_POSIX_compliance_of_Linux_distributions" rel="nofollow noreferrer">Dash</a> on Debian) and is quite readable, but that's a matter of taste:
<pre><code>if [ -n &quot;$1&quot; ]; then
 cat &quot;$1&quot;
else
 cat
fi | commands_and_transformations
</code></pre>
Details: If the first parameter is non-empty then <code>cat</code> that file, else <code>cat</code> standard input. Then the output of the whole <code>if</code> statement is processed by the <code>commands_and_transformations</code>.

blocks|key|816893|text|这个很容易在终端上使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|816894|$+echo+'1\n2\n3\n'+%7C+while+read+-r;+do+echo+$REPLY;+done
1
2
3|code-block|syntax|javascript|816895|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This one is easy to use on the terminal:

<pre><code>$ echo '1\n2\n3\n' | while read -r; do echo $REPLY; done
1
2
3
</code></pre>

blocks|key|816559|text|使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|816560|for+line+in+`cat`;+do
++++something($line);
done|code-block|syntax|javascript|816561|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Use:
<pre><code>for line in `cat`; do
 something($line);
done
</code></pre>

The following Perl script (<code>my.pl</code>) can read from either the file in the command line arguments or from <a href="https://en.wikipedia.org/wiki/Standard_streams#Standard_input_(stdin)" rel="noreferrer">standard input</a> (STDIN):
<pre><code>while (&lt;&gt;) {
 print($_);
}
</code></pre>
<code>perl my.pl</code> will read from standard input, while <code>perl my.pl a.txt</code> will read from <code>a.txt</code>. This is very handy.
Is there an equivalent in Bash?

How to read from a file or standard input in Bash

Debian

Perl

以下Perl脚本(my.pl)可以从命令行参数中的文件读取，也可以从 (STDIN)读取：while (<>) { print($_);}perl my.pl将从标准输入读取，而perl my.pl a.txt将从a.txt读取。这非常方便。在Bash中有没有类似的东西？

问如何在Bash中读取文件或标准输入
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回答 13

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