[Bug 1920967] [NEW] Bash not interpreting negative offsets in Substrring Expanison of parameters

[Kevin O'Gorman]

Public bug reported:

According to the man page, $(variable:offset[:length]} should treat
negative offsets as counting from the end of the value.  Instead, I find
any such substring expansion expands the ENTIRE variable regardless of
the exact negative offset or any length provided.

A short typescript is attached.  It shows two good expansions followed
by three bad ones.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: bash 5.0-6ubuntu1.1
ProcVersionSignature: Ubuntu 5.4.0-66.74-generic 5.4.86
Uname: Linux 5.4.0-66-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.11-0ubuntu27.16
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: XFCE
Date: Tue Mar 23 09:09:28 2021
SourcePackage: bash
UpgradeStatus: Upgraded to focal on 2021-02-19 (32 days ago)

** Affects: bash (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug focal

** Attachment added: "showing what happens when I try it"
   https://bugs.launchpad.net/bugs/1920967/+attachment/5480253/+files/typescript

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https://bugs.launchpad.net/bugs/1920967

Title:
  Bash not interpreting negative offsets in Substrring Expanison of
  parameters

Status in bash package in Ubuntu:
  New

Bug description:
  According to the man page, $(variable:offset[:length]} should treat
  negative offsets as counting from the end of the value.  Instead, I
  find any such substring expansion expands the ENTIRE variable
  regardless of the exact negative offset or any length provided.

  A short typescript is attached.  It shows two good expansions followed
  by three bad ones.

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: bash 5.0-6ubuntu1.1
  ProcVersionSignature: Ubuntu 5.4.0-66.74-generic 5.4.86
  Uname: Linux 5.4.0-66-generic x86_64
  NonfreeKernelModules: wl
  ApportVersion: 2.20.11-0ubuntu27.16
  Architecture: amd64
  CasperMD5CheckResult: skip
  CurrentDesktop: XFCE
  Date: Tue Mar 23 09:09:28 2021
  SourcePackage: bash
  UpgradeStatus: Upgraded to focal on 2021-02-19 (32 days ago)

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