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copied!<p>For Perl single character <a href="http://perldoc.perl.org/perlrebackslash.html" rel="nofollow">backslash escapes</a>, you can do this safely using a two character <code>eval</code> as part of the substitution. You need to put in the characters that are acceptable to interpret in the character class after the <code>\</code>, and then the single character after is <code>eval</code>'d and inserted into the string. </p> <p>Consider:</p> <pre><code>#!/usr/bin/perl use warnings; use strict; print "\n\n\n\n"; while (my $data = <DATA>) { $data=~s/\\([rnt'"\\])/"qq|\\$1|"/gee; print $data; } __DATA__ Hello!\nI\'d like to tell you a little \"secret\". A backslask:\\ Tab'\t'stop line 1\rline 2 (on Unix, "line 1" will get overwritten) line 3\\nline 4 (should result in "line 3\\nline 4") line 5\r\nline 6 </code></pre> <p>Output:</p> <pre><code>Hello! I'd like to tell you a little "secret". A backslask:\ Tab' 'stop line 2 (on Unix, "line 1" will get overwritten) line 3\nline 4 (should result in "line 3\nline 4") line 5 line 6 </code></pre> <p>The line <code>s/\\([rnt'"\\])/"qq|\\$1|"/gee</code> does the work. </p> <ul> <li><p>The <code>\\([rnt'"\\])</code> has the acceptable characters to eval inside the braces.</p></li> <li><p>The <code>gee</code> part does a double eval on the replacement string. </p></li> <li><p>The <code>"qq|\\$1|"</code> part is eval'd twice. The first <code>eval</code> replaces <code>$1</code> into the string, and the second performs the interpolation. </p></li> </ul> <p>I cannot think of a two character combination here that would be a security breach...</p> <p>This method does <em>not</em> deal with the following properly:</p> <ul> <li><p>Quoted strings. For example, Perl would not unescape the string 'line 1\nline 2' because of the single quotes.</p></li> <li><p>Escapes sequences that are longer than a single character, such as hex <code>\x1b</code> or Unicode such as <code>\N{U+...}</code> or control sequences such as <code>\cD</code></p></li> <li><p>Anchored escapes, such as \LMAKE LOWER CASE\E or \Umake upper case\E</p></li> </ul> <p>If you want more complete escape replacement, you can use this regex:</p> <pre><code>#!/usr/bin/perl use warnings; use strict; print "\n\n\n\n"; binmode STDOUT, ":utf8"; while (my $data = <DATA>) { $data=~s/\\( (?:[arnt'"\\]) | # Single char escapes (?:[ul].) | # uc or lc next char (?:x[0-9a-fA-F]{2}) | # 2 digit hex escape (?:x\{[0-9a-fA-F]+\}) | # more than 2 digit hex (?:\d{2,3}) | # octal (?:N\{U\+[0-9a-fA-F]{2,4}\}) # unicode by hex )/"qq|\\$1|"/geex; print $data; } __DATA__ Hello!\nI\'d like to tell you a little \"secret\". Here is octal: \120 Here is UNICODE: \N{U+0041} and \N{U+41} and \N{U+263D} Here is a little hex:\x50 \x5fa \x{5fa} \x{263B} lower case next char \lU \lA upper case next char \ua \uu A backslask:\\ Tab'\t'stop line 1\rline 2 (on Unix, "line 1" will get overwritten) line 3\\nline 4 (should result in "line 3\\nline 4") line 5\r\nline 6 </code></pre> <p>That handles all Perl <a href="http://perldoc.perl.org/perlrebackslash.html" rel="nofollow">escapes</a> except: </p> <ol> <li><p>Anchored type (\Q, \U, \L ended by \E)</p></li> <li><p>Quoted forms, such as <code>'don't \n escape in single quotes'</code> or <code>[not \n in here]</code></p></li> <li><p>named unicode characters, such as <code>\N{THAI CHARACTER SO SO}</code></p></li> <li><p>Control characters like <code>\cD</code> (that is easily added...)</p></li> </ol> <p>But that was not part of your question as I understood it...</p>

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