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POCommon gotchas for Perl?
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copied!<p>The question on <a href="https://stackoverflow.com/questions/161872/hidden-features-of-perl">Hidden features of Perl</a> yielded at least <a href="https://stackoverflow.com/questions/161872/hidden-features-of-perl#162249">one response</a> that could be regarded as either a feature or a mis-feature. It seemed logical to follow up with this question: what are common non-obvious mistakes in Perl? Things that seem like they ought to work, but don't.</p> <p>I won't give guidelines as to how to structure answers, or what's "too easy" to be considered a gotcha, since that's what the voting is for.</p> <h2>Table of Answers</h2> <p><strong>Syntax</strong></p> <ul> <li>General <ul> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#166660">Single quotes instead of <code>::</code> in identifiers</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#167418">Indirect object syntax</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#166698">Confusing references with plain var types</a></li> </ul></li> <li>Filehandles <ul> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#167342">Heredoc notation when using print with lexical filehandles</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#167122">Printing to a lexical filehandle contained in a hash</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#175231"><code>my</code> declarations should use parens around lists of variables</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas/549685#549685">Comparing strings with == and !=</a></li> </ul></li> </ul> <p><strong>Semantics/Language Features</strong></p> <ul> <li>General <ul> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#167064"><code>do</code> is not a loop. You cannot <code>next</code>.</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#166804">Using the /o modifier with a regex</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas/1037460#1037460">Forgetting that <code>readdir</code>'s results are not relative to the CWD</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas/1373613#1373613">Unary minus's interaction with strings</a></li> </ul></li> <li>Context <ul> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#166702">Assignment to scalar from arrays vs. lists</a></li> <li><a href="https://stackoverflow.com/questions/146329/what-is-the-worst-gotcha-youve-experienced#146394">The glob() iterator</a> (On a different question)</li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#175224">Implicit returns in list context</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#427595">Parenthesis changing the semantics of operators</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas/549324#549324">Calling context is propagated to return statements within functions</a></li> </ul></li> <li>Variables <ul> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#166778">Can't localize exported variables without exporting the entire typeglob</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#167410">Using multiple variables (of different types) with the same name</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#167505"><code>while <FH></code> does not localize <code>$_</code> automatically</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#167219">The Variable That's Validly Zero</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#169373">Constants can be redefined</a></li> </ul></li> </ul> <p><strong>Debugging</strong></p> <ul> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#175285">Warning: Use of uninitialized value in concatenation</a></li> </ul> <p><strong>Best Practices</strong></p> <ul> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#166682">Forgetting to <code>use strict</code> and <code>use warnings</code> (or <code>use diagnostics</code>)</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#169391">Misspelling variable names</a> (i.e., <code>use strict</code>, again)</li> </ul> <p><strong>Meta-Answers</strong></p> <ul> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#168905">The perltrap manpage</a></li> <li><a href="https://stackoverflow.com/questions/166653/perl-common-gotchas#169443">Perl::Critic</a></li> </ul> <p>See Also: <a href="https://stackoverflow.com/questions/66117/aspnet-common-gotchas">ASP.NET - Common gotchas</a></p>

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