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category-morning-pages"> + <h2 class="entry-title">Why `sed -i’ exists</h2> + <div class="entry-meta"> + <span class="meta-prep meta-prep-author">Posted on</span> <a href="http://lukeshu.ath.cx/1/wordpress/2011/05/why-sed-i-exists/" title="05:21" rel="bookmark"><span class="entry-date">2011/05/27</span></a> <span class="meta-sep">by</span> <span class="author vcard"><a class="url fn n" href="http://lukeshu.ath.cx/1/wordpress/author/lts/" title="View all posts by lts">lts</a></span> + </div><!-- .entry-meta --> + <div class="entry-content"> +<p>I’ve decided to to a morning-pages type thing here, just to get info out. This means that I’ll be posting 250-ish word weblog post<br /> +snippits sharing whatever, and fairly frequently posting, if this works.</p> +<p>So, what is the purpose of the <code>-i</code> flag to <code>sed</code>? Simply, it edits the file in place, instead of dumping the edit to stdout.</p> +<p>Those of you familiar with “<code>cat -v</code> Considered Harmful” or just traditional UNIX design will say “bah, what a useless flag, just use <code>sed 's/regex//' < file > file</code> to write the changes back to the file.</p> +<p>But there’s a problem with this. There is a race condition, the file has been opened twice, once for reading, and once for writing. If they get closed in the wrong order, you will end up with an empty file. In my experience this very seldom happens. However, when you have a shell script that usually works, but just occaisionally corrupts your `database’, you’ll see why <code>sed -i</code>‘s important.</p> + + </div><!-- .entry-content --> + <div class="entry-links"> + + </div> + + <div class="entry-utility"> + This entry was posted in <a href="http://lukeshu.ath.cx/1/wordpress/category/computers/" title="View all posts in Computers" rel="category tag">Computers</a>, <a href="http://lukeshu.ath.cx/1/wordpress/category/morning-pages/" title="View all posts in morning-pages" rel="category tag">morning-pages</a>. Bookmark the <a href="http://lukeshu.ath.cx/1/wordpress/2011/05/why-sed-i-exists/" title="Permalink to Why `sed -i’ exists" rel="bookmark">permalink</a>. + + </div><!-- .entry-utility --> + </div><!-- #post-## --> + + <div id="nav-below" class="navigation"> + <div class="nav-previous"><a href="http://lukeshu.ath.cx/1/wordpress/2011/02/questions-about-copyright-of-the-deceased/" rel="prev"><span class="meta-nav">←</span> Questions about copyright of the deceased</a></div> + <div class="nav-next"><a href="http://lukeshu.ath.cx/1/wordpress/2011/08/emacs-autopair-problems-when-using-term-mode/" rel="next">[Emacs] autopair problems when using term-mode <span class="meta-nav">→</span></a></div> + </div><!-- #nav-below --> + + + + <div id="comments"> + <div id="respond"> + <h3 id="reply-title">Leave a Reply <small><a rel="nofollow" id="cancel-comment-reply-link" href="/1/wordpress/2011/05/why-sed-i-exists/#respond" style="display:none;">Cancel reply</a></small></h3> + <form action="http://lukeshu.ath.cx/1/wordpress/wp-comments-post.php" method="post" id="commentform"> + <p class="comment-notes">Your email address will not be published. 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