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[PATCH] Fix leaked internal escapes of patsub_replacement ${var/$pat/"&"

From: Koichi Murase
Subject: [PATCH] Fix leaked internal escapes of patsub_replacement ${var/$pat/"&"} with pat=# or pat=%
Date: Mon, 18 Jul 2022 15:11:57 +0900

Here is another patch that was pending.

Bash Version: 5.2
Commit 87a6e89edc7cb1af057e2c15666df189595d305b (the current devel)


  When `shopt -s patsub_replacement' is turned on and the pattern
  string `pat' of ${var/$pat/"&"} is just an anchoring character `#'
  or `%', the internal escape of `&' (i.e., `\&') remains in the
  result of the parameter expansion.  Also, with the same condition,
  the unquoted & in ${var/$pat/&} remains a literal & where we expect
  it to be expanded to an empty string.


  When `pat' contains non-anchoring characters, the expected result of
  the expansions is obtained as

  $ bash-dev --norc
  $ shopt -s patsub_replacement
  $ v=1234 pat=2; echo "${v/$pat/<&>}, ${v/$pat/<\&>}, ${v/$pat/"<&>"}"
  1<2>34, 1<&>34, 1<&>34
  $ v=1234 pat=#1; echo "${v/$pat/<&>}, ${v/$pat/<\&>}, ${v/$pat/"<&>"}"
  <1>234, <&>234, <&>234

  Here, unquoted & in the replacement is expanded to the matched
  string as expected while quoted &'s are expanded to the literal `&'.
  However, only when pat=# or pat=%, the result becomes

  $ v=1234 pat=#; echo "${v/$pat/<&>}, ${v/$pat/<\&>}, ${v/$pat/"<&>"}"
  <&>1234, <\&>1234, <\&>1234

  where unquoted & does not become an empty string, and quoted &'s
  become \&.  In particular, with ${v/$pat/"<&>"}, a backslash
  originally not present is inserted in the expanded result.  I
  instead expect the following result for consistency with the other

  <>1234, <&>1234, <&>1234


  I attach a patch `r0031-fix-patsub.patch.txt'.

  I guess the original intent of the related code has been to disable
  patsub_replacement for ${var/#/...} and ${var/%/...} where the
  pattern `# + <empty string>' or `% + <empty string>' is explicitly
  specified (not through a parameter expansion $pat), but I would
  still think we should keep the special treatment of unquoted & for
  these cases as well when patsub_replacement is turned on for
  consistency with other cases.


Attachment: r0031-fix-patsub.patch.txt
Description: Text document

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