[Bug 1045072] [NEW] bash generates spurious DEL on empty variable interpolation

[Ian! D. Allen]

Public bug reported:

#!/bin/bash -u
# BASH BUG: spurious DEL characters appear on empty variable interpolation.
# BASH 4.2.8(1)-release
# Script works fine (expected output) using /bin/dash.
# -Ian! D. Allen - idallen at idallen.ca - www.idallen.com

a=''

{
echo correct "$a"               # correct empty output line
echo correct "$a""$a"           # correct empty output line
echo correct "$a""$a""$a"       # correct empty output line
echo XwrongX "$a""$a""$a""$a"   # spurious two DEL chars appear at line end
echo correct a"$a"              # correct single "a" on line
echo XwrongX a"$a""$a"          # spurious DEL char appears at line end
echo correct a"$a$a"            # correct single "a" on line
echo correct a"$a$a$a$a"        # correct single "a" on line
} | cat -v

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: bash 4.2-0ubuntu3
ProcVersionSignature: Ubuntu 2.6.38-15.66-generic 2.6.38.8
Uname: Linux 2.6.38-15-generic x86_64
Architecture: amd64
Date: Sun Sep  2 15:36:55 2012
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
SourcePackage: bash
UpgradeStatus: No upgrade log present (probably fresh install)

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


** Tags: amd64 apport-bug natty

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https://bugs.launchpad.net/bugs/1045072

Title:
  bash generates spurious DEL on empty variable interpolation

Status in “bash” package in Ubuntu:
  New

Bug description:
  #!/bin/bash -u
  # BASH BUG: spurious DEL characters appear on empty variable interpolation.
  # BASH 4.2.8(1)-release
  # Script works fine (expected output) using /bin/dash.
  # -Ian! D. Allen - idallen at idallen.ca - www.idallen.com

  a=''

  {
  echo correct "$a"               # correct empty output line
  echo correct "$a""$a"           # correct empty output line
  echo correct "$a""$a""$a"       # correct empty output line
  echo XwrongX "$a""$a""$a""$a"   # spurious two DEL chars appear at line end
  echo correct a"$a"              # correct single "a" on line
  echo XwrongX a"$a""$a"          # spurious DEL char appears at line end
  echo correct a"$a$a"            # correct single "a" on line
  echo correct a"$a$a$a$a"        # correct single "a" on line
  } | cat -v

  ProblemType: Bug
  DistroRelease: Ubuntu 11.04
  Package: bash 4.2-0ubuntu3
  ProcVersionSignature: Ubuntu 2.6.38-15.66-generic 2.6.38.8
  Uname: Linux 2.6.38-15-generic x86_64
  Architecture: amd64
  Date: Sun Sep  2 15:36:55 2012
  InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
  SourcePackage: bash
  UpgradeStatus: No upgrade log present (probably fresh install)

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