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    <pre><code>cat dirs.txt | while read dir; do ls -al "$dir" done </code></pre> <ol> <li><p>When you use the backtick operator the output is split into tokens at each whitespace character. <code>read</code>, on the other hand, will read one line at a time rather than one word at a time. So the solution, which looks kind of odd, is to pipe the file into the loop so it can be read line by line.</p></li> <li><p>You need to quote <code>"$dir"</code> in the <code>ls</code> command so that the entire file name, whitespace and all, is treated as a single argument. If you don't do that <code>ls</code> will see two file names, <code>/var/tmp/old</code> and <code>files.txt</code>.</p></li> </ol> <p>I'm probably going to get awarded the <a href="http://www.partmaps.org/era/unix/award.html" rel="noreferrer">Useless Use of Cat Award</a>. You can simplify this even further by removing the <code>cat</code>:</p> <pre><code>while read dir; do ls -al "$dir" done &lt; dirs.txt </code></pre> <p>This works because the <strong>entire</strong> <code>while</code> loop acts like one big command, so just like you can pipe <code>cat</code> into it, you can also use file redirection.</p> <hr> <h2>Taking it even further...</h2> <p>Depending on how <code>dirs.txt</code> is generated you may just be able to get rid of it entirely and do everything in one command. If it's just a temporary file you could eliminate it by piping the command generates <code>dirs.txt</code> into the <code>while</code> loop directly, skipping the temporary file. For instance, replace</p> <pre><code>find /var -name '*old*' &gt; dirs.txt while read dir; do ls -al "$dir" done &lt; dirs.txt </code></pre> <p>with</p> <pre><code>find /var -name '*old*' | while read dir; do ls -al "$dir" done </code></pre> <p>Pretend <code>find</code> is whatever command you're doing to generate the file list.</p> <p>And actually, if you are in fact using <code>find</code> you can probably do everything in one big <code>find</code> command without any loops or anything! For example, the above code using <code>find</code> and <code>while</code> could be done with a single <code>find</code> command like this:</p> <pre><code>find /var -name '*old*' -exec ls -al {} \; </code></pre> <p><code>find</code> is a really flexible command that can both search for files matching all kinds of complicated criteria, and pass those files as command-line arguments to other commands using the <code>-exec</code> option. When you use <code>-exec</code> the <code>{}</code> gets replaced with each file name.</p>
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    1. POFor loop using find lacks doesn't properly handle directory names having white space character
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    1. USJohn Kugelman
    1. USJohn Kugelman
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    1. CONote that there's a potential gotcha with any of the "somecommand | while read..." versions: the while loop runs in a subshell, so any variables set in it vanish as soon as it exits. The "while ... done <dirs.txt" versions don't have this problem. See http://mywiki.wooledge.org/BashFAQ/024 for some workarounds.
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      1. USGordon Davisson
    2. COAnd bash's [process substitution](http://www.gnu.org/software/bash/manual/bashref.html#Process-Substitution) allows you to avoid the temp file: `while read -r line; do ... done < <(find ...)`
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      1. USglenn jackman
 

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