Beginning Web Development With Perl : From Novice to ... - Nabo

APPENDIX ■ PERL BASICS 289print '\ tThis is a single-quoted string.\ n';print "\ tThis is a double-quoted string.\ n";The double-quoted string will have its escape sequences processed, and the singlequotedstring will not. The output is$ perl quotes.pl\ tThis is a single quoted string.\ n This is a double-quoted string.$What do we do if we want to have a backslash in a string? This is a common concern forWindows users, as a Windows path looks something like this: C:\ WINNT\ Profiles\. . .. Ina double-quoted string, a backslash will start an escape sequence, which is not what we wantit to do.There is, of course, more than one way to do it. We can either use a single-quoted string,as shown previously, or we can escape the backslash. One principle that you’ll see often inPerl, and especially when you get to regular expressions, is that you can use a backslash toturn off any special effect a character may have. This operation is called escaping or, morecommonly, backwhacking.In this case, we want to turn off the special effect a backslash has, and so we escape it:#!/usr/bin/perl -w# quotes2.plprint "C:\ \ WINNT\ \ Profiles\ \ \ n";print 'C:\ WINNT\ Profiles\ ', "\ n";This prints the following:$ perl quotes2.plC:\ WINNT\ Profiles\C:\ WINNT\ Profiles\$Aha! Some of you may have gotten this message instead:Can't find string terminator " ' " anywhere before EOF at quotes2.pl line 5.The reason for this is that you probably left out the space character in line 5 before thesecond single quote. Remember that \ ' tells Perl to escape the single quote, and so it merrilyheads off to look for the next quote, which of course is not there. Try this program to see howPerl treats these special cases:#!/usr/bin/perl -w# aside1.plprint 'ex\ \ er\ \ ' , ' ci\ ' se\ '' , "\ n";The output you get this time is$ perl aside1.plex\ er\ ci' se'$