[Bug 1618224] Re: Single quote character not handled well in associative array index

[xhienne]

Not a bug IMHO, but that may be open to debate. At least the observed behavior conforms to the bash manual which reads:
- ((expression)) is strictly equivalent to: let "expression"
- parameter expansion is performed _before_ the expression is evaluated

Therefore, ((++a[$b])) translates to let "++a[$b]" which translates to
let "++a[80's]" which leads to an error.

The proper syntax would be (('++a[$b]')) which is admittedly quite
counter-intuitive. This way '$b' is evaluated as a whole during the
arithmetic evaluation.

Demonstration:
$ declare -A a
$ b="80's"
$ (('++a[$b]'))
$ printf '%s\n' "${!a[@]}" "${a[@]}"
80's
1
$ (('++a[$b]'))
$ printf '%s\n' "${!a[@]}" "${a[@]}"
80's
2

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https://bugs.launchpad.net/bugs/1618224

Title:
  Single quote character not handled well in associative array index

Status in bash package in Ubuntu:
  New

Bug description:
  Say you have script named test.sh in current directory

  #!/bin/bash
  declare -A a
  b="80's"
  ((++a[$b]))
  ((++a["$b"]))
  [[ $((++a[$b])) ]] || true
  [[ $((++a["$b"])) ]] || true
  echo ${a["$b"]}
  echo ${a[$b]}

  It outputs

  ./test.sh: line 4: ((: ++a[80's]: bad array subscript (error token is "a[80's]")
  ./test.sh: line 5: ((: ++a[80's]: bad array subscript (error token is "a[80's]")
  ./test.sh: line 6: ++a[80's]: bad array subscript (error token is "a[80's]")
  1
  1

  Expected output is

  4
  4

  like it is when b is "80s". Note that only the incremention on line 7 of the script works.
  This bug also happens by bash 4.3-7ubuntu1.5 (Trusty)

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: bash 4.3-14ubuntu1.1
  ProcVersionSignature: Ubuntu 4.4.0-31.50-generic 4.4.13
  Uname: Linux 4.4.0-31-generic x86_64
  NonfreeKernelModules: nvidia_uvm nvidia
  ApportVersion: 2.20.1-0ubuntu2.1
  Architecture: amd64
  CurrentDesktop: XFCE
  Date: Tue Aug 30 00:24:58 2016
  EcryptfsInUse: Yes
  InstallationDate: Installed on 2015-11-21 (282 days ago)
  InstallationMedia: Xubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
  SourcePackage: bash
  UpgradeStatus: Upgraded to xenial on 2016-06-24 (66 days ago)

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