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PO$? inside bash trap
 

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    <p>From a bash script, I'm trying to handle segmentation faults from a c++ program. I've read that using <code>trap</code> on <code>SIGCHLD</code> can be used for this purpose. Inside the trap I should be able to test for <code>$?</code> to get the return code from the program. See <a href="https://unix.stackexchange.com/questions/24307">https://unix.stackexchange.com/questions/24307</a> for example.</p> <p>It's not working for me, and I can't figure out why.</p> <p>Here is the script:</p> <pre><code>#! /bin/bash set -bm trap 'echo "Trap result code $?"' CHLD echo "Script: starting program" ./sigsegv echo "Script: result code from program was $?" </code></pre> <p>As you might guess, the <code>sigsegv</code> program just causes a segfault:</p> <pre><code>#include &lt;csignal&gt; #include &lt;iostream&gt; using namespace std; int main(int argc, char** argv) { cout &lt;&lt; "C++ will now cause a SIGSEGV" &lt;&lt; endl; raise(SIGSEGV); cout &lt;&lt; "After signal -- shouldn't get here" &lt;&lt; endl; return 0; } </code></pre> <p>When I run the wrapper script, I get this:</p> <pre><code>$./wrappersimple.sh Script: starting program C++ will now cause a SIGSEGV Trap result code 0 ./wrapper.sh: line 8: 26368 Segmentation fault (core dumped) ./sigsegv Script: result code from program was 139 </code></pre> <p>The key piece was <code>Trap result code 0</code>. That's where I expected it to say 139 to indicate a SIGSEGV (which is 128 base value + 11 for SIGSEGV).</p> <p>In case it matters, RHEL 6.2, bash 4.1.2(1)-release.</p>
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