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Re^7: Escaping multiple escape chars

by ikegami (Patriarch)
on Dec 12, 2005 at 15:50 UTC ( [id://516036]=note: print w/replies, xml ) Need Help??


in reply to Re^6: Escaping multiple escape chars
in thread Escaping multiple escape chars

However, 'some\\text' and "some\\text" don't behave as you would expect

I got the following (abbreiviated) results:

Case 1 'some\text': some\text ------- PV = 0x1aa01f0 "some\\text"\0 Case 2 'some\\text: some\text ------- PV = 0x1aa01f0 "some\\text"\0 Case 3 "some\text": some ext ------- PV = 0x1aa01f0 "some\text"\0 Case 4 "some\\text": some\text ------- PV = 0x1aa01f0 "some\\text"\0

If you obtained the above, perl behaved as expected (or at least as documented). According to to the relevant docs,

double-quoted string literals are subject to backslash and variable substitution; single-quoted strings are not (except for \' and \\).

In single quotes, perl interprets the backslash literally (instead of an escape) unless followed by another backslash or by a single quote. This DWIM most of the time, since few characters ever need to be escaped in single-quoted strings. For example, '\n' results in the string {backslash}+{lowercase n}.

In double quotes, perl interprets the backslash and the following character as an escape (instead of literally). How perl interprets an invalid/unrecognized escape sequence is undocumented (or unclearly documented), but the behaviour has consistently been to replace the escape sequence with the character that followed the backslash. This DWIM most of the time, since the extra backslash was probably a case of overzealous escaping. For example, "\<" results in the string {right angle bracket}.

If you don't see the necessity of the equivalency of
"some\\text"
and
'some\\text'
try answering the following questions:

  • How would you code the string {backslash}+{backslash} using single quotes?
  • How would you code the string {backslash}+{backslash} using double quotes?
  • How would you code the string {backslash}+{backslash}+{single quote} using single quotes?
  • How would you code the string {backslash}+{backslash}+{double quote} using double quotes?
  • How would you code the string {backslash}+{single quote} using single quotes?
  • How would you code the string {backslash}+{double quote} using double quotes?

Replies are listed 'Best First'.
Re^8: Escaping multiple escape chars
by JamesNC (Chaplain) on Dec 12, 2005 at 17:03 UTC
    You make an excellent point(s) and I really appreciate your lengthy discussion of this with me. I think I have learned a very important lesson lesson (doesn't always DWIM inside of '').
    How would I code it? I don't think for 1 second that I could do a better job than those who faced this problem. But, I would love to try. I would have to see how it is done now. I know in coding, sometimes you paint yourself in a corner and for architecture reasons these things happen as artifacts of the design, and it cannot be changed.
    Thanks soooo much for discussing this with me.
    Regards,
    JamesNC

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