Debian Bug report logs - #850202
dash: test with multiple conditions cannot handle variable whose expanded value is same as an operator

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Message #5 received at submit@bugs.debian.org (full text, mbox, reply):

From: J G Miller <miller@yoyo.ORG>

To: Debian Bug Tracking System <submit@bugs.debian.org>

Subject: dash: test with multiple conditions cannot handle variable whose expanded value is same as an operator

Date: Thu, 05 Jan 2017 00:53:57 +0100

Package: dash
Version: 0.5.7-4+b1
Severity: normal

In Bourne shell script with dash, using either [ ] or test,

   test -n "${variable}" && echo "variable is set to -->${variable}<--"

works as expected even if the value of variable is to a value the same
as a test operator eg -ne or -nt

   variable="-ne" ; test -n "${variable}" && echo "variable is set to -->${variable}<--"
   variable is set to -->-ne<--

However the addition of another test condition with -a or -o results in an
unexpected behavior in that the expanded variable is now treated as an operator
and not just as the string as should be the case.

    variable="-ne" ; test -n "${variable}" -a -n "${DISPLAY}" && echo "variable is set to -->${variable}<--"
    dash: 1: test: Illegal number: -n

Applying quoted parentheses makes no difference.

    variable="-ne" ; test \( -n "${variable}" \) -a \( -n "${DISPLAY}" \) && echo "variable is set to -->${variable}<--"
dash: 2: test: Illegal number: -n

Similarly bad behavior is seen with a variable set to "-nt", which is how I stumbled upon this problem.

    variable="-nt" ; test \( -n "${variable}" \) -a \( -n "${DISPLAY}" \) && echo "variable is set to -->${variable}<--"
dash: 3: test: closing paren expected

So if the test is consists of a single condtion, the expanded variable does not cause
problems with the test, and should not affect the test if it is part of a multiple condition test.

Incidentally bash also has this problem.

So the short term kludge in a shell script is to do

     if [ -n "${variable_with_problem_value}" ]
     then
          if [ \( other_condition1 \) -a \( other_condition2 \) ]
          then
               ...



-- System Information:
Debian Release: 8.6
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: armel (armv5tel)

Kernel: Linux 3.16.0-4-kirkwood
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=ANSI_X3.4-1968) (ignored: LC_ALL set to C)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages dash depends on:
ii  debianutils  4.4+b1
ii  dpkg         1.17.27
ii  libc6        2.19-18+deb8u6

dash recommends no packages.

dash suggests no packages.

-- debconf information:
* dash/sh: true

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