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Re: [DOC] Incomplete explanation about the regex =~ operator

From: kevin
Subject: Re: [DOC] Incomplete explanation about the regex =~ operator
Date: Sat, 12 Jan 2019 07:14:47 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

Le 09/01/2019 à 21:37, Chet Ramey a écrit :
On 1/9/19 2:27 PM, kevin wrote:
My message was poorly formatted (I lack of experience) and consequently you
misunderstood it.
The shell operation is unusual when a regular expression appears inside a
conditional expression. Indeed, neither the Bash man page or the Bash
Reference Manual indicates that the shell quotes some characters internally
(Bash FAQ: http://git.savannah.gnu.org/cgit/bash.git/tree/doc/FAQ#n1927).
"Any part of  the  pat-
  tern  may be quoted to force the quoted portion to be matched as
  a string."

Moreover, the explanation in the Bash FAQ is unclear; it lacks examples to
know when "an interference" occurred.
What is "an interference"?

Look at the following answer to get an overview of the issue:
That answer is correct: bash uses the C library's regexp library and
only guarantees that POSIX EREs work.

I do not speak English very well.

The Bash FAQ indicates that the shell works differently in a conditional expression formed using

a regular expression. Nonetheless, the Bash FAQ does not give examples to get a concrete idea.

|"In versions of bash prior to bash-3.2, the effect of quoting the regular expression argument to the [[ command's =~ operator was not specified. *The practical effect* was that double-quoting the pattern argument required backslashes to quote special pattern characters, *which interfered with* the backslash processing performed by double-quoted word expansion and was inconsistent with how the == shell pattern matching operator treated quoted characters."|

I do not see the practical effect because I do not find concrete cases (or examples). In other words, I do not understand the justification.

Finally, the fact that the shell works differently in the mentioned case should be indicated in the man page and Texinfo source.

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