Actually, that is not the message I see (nor quite what I would expect). I see:

Backslash found where operator expected at noname.pl line 5, near "s//
+/\"
syntax error at noname.pl line 5, near "s///\"
Search pattern not terminated at noname.pl line 5.

[download]

The rule is: resolve the first error first. Perl is expecting to see either flag characters or a termination character such as ; - Perl doesn't expect to see a \, it makes no sense there.

What were you trying to achieve with the regex substitution? Replace the / with \? Instead try:

$a =~ s!/!\\!g;

[download]

Note the use if ! to delimit the regex so that / can be used unquoted, and also that \ needs to be quoted.

BTW: avoid the use of $a and $b except in the special context of sort.

DWIM is Perl's answer to Gödel

In reply to Re: Problem in sustitution of a string by GrandFather
in thread Problem in sustitution of a string by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.