[Bug 141481] Re: dash as #!/bin/sh introduces countless incompatibilities

[Victor Mitin]

There is one more DASH bug.

Described here:
http://groups.google.com/group/vim_use/browse_thread/thread/837988813a06c280/f8b4aadd575affaa?lnk=gst&q=expect#f8b4aadd575affaa

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https://bugs.launchpad.net/bugs/141481

Title:
  dash as #!/bin/sh introduces countless incompatibilities

Status in “dash” package in Ubuntu:
  Invalid

Bug description:
  Binary package hint: dash

  Hi,
  I understand the rationale of using a lightweight bourne shell clone for #!/bin/sh instead of bash, however Ubuntu's use of dash as #!/bin/sh by default has broken countless scripts and brought us back into the dark ages of platform-specific scripting. Bashisms and various unixy  #!/bin/sh variant quirks are well understood in their incomatabilites (especially by the autoconf/autopackage people), except this new player - dash.

  Software vendors, open source projects and even the ubuntu BTS are flooded with bugs that stem from dash incompatabilites, which are often hard to debug the root cause of. Examples:
  https://bugs.launchpad.net/ubuntu/+source/dash/+bug/92189
  https://bugs.launchpad.net/ubuntu/+source/dash/+bug/105634
  https://bugs.launchpad.net/ubuntu/+source/dash/+bug/71887
  https://bugs.launchpad.net/ubuntu/+source/dash/+bug/135863
  https://bugs.launchpad.net/ubuntu/+source/dash/+bug/128730

  This is not a duplicate bug report - it the a compound of all the above bugs that 
  Examples of 3rd party apps that break:
  the ATI installer, vmWare, Xen, Mathematica, NX Server, MKS, NVC and anything else that relies on a sane #!/bin/sh

  The scope of this problem is rather large. It would be reasonable to
  say "fix the scripts" if the scripts were buggy, but alas this is not
  the case.

  The following code snippets are extracted from live, working scripts
  that are used frequently, that work in other versions of #!/bin/sh,
  but break in dash:

  $ dash -c 'cnt=6; while [ $((cnt = cnt - 1)) -gt 0 ]; do echo $cnt; done'
  dash: arith: syntax error: "cnt = cnt - 1"

  $ dash-c 'if false; then d="${foo/bar}"; fi'
      dash: Syntax error: Bad substitution

  $ dash -c 'a=water;echo ${a:2:2}'
  dash: Syntax error: Bad substitution

  $ dash -c 'exec 20<&0'
  exec: 1: 20: not found

  $ dash -c 'echo $UID'
  # no output. how on earth are we supposed to safely and portably get the UID?

  $ dash -c 'echo hello 2>&1>/dev/null'
  dash: Syntax error: redirection unexpected

  $ dash -c 'x="1 2"; local y=$x; echo $y'
  local: 1: 2: bad variable name

  And an example from makeself:
  shh.sh:
  #!/bin/sh
  tmpfile=foo
  tmpdir=/tmp/dashtmp
  mkdir "$tmpdir"
  ( cd "$tmpdir" && ( tar cvf - . | eval "gzip -c9" ) >> "$tmpfile" ) || { echo "Failed"; exit 1; }
  echo >> "$tmpfile" >&-

  $ ./shh.sh
  ./
  ./foo
  ./shh: line 6: echo: write error: Bad file descriptor

  I invite others to collect similar examples here. If Ubuntu will not
  fix dashisms then we must support dash, which is why a compilation of
  incompatabilities is necessary, so that a list of workarounds can be
  put together, à la
  http://www.gnu.org/software/autoconf/manual/html_node/Portable-
  Shell.html, http://code.dogmap.org/lintsh/ and http://steve-
  parker.org/sh/sh.shtml which mostly cover outdated incompatabilites
  between other shells.

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