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POIncrementing a variable triggers EXIT in bash 4, but not in bash 3
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  1. POIncrementing a variable triggers EXIT in bash 4, but not in bash 3
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    copied!<p>Consider this (exemplary) bash script:</p> <pre><code>#!/bin/bash -e errorExit() { echo "" &gt;&amp;2 echo "ERROR (${var_scriptfilename}):" &gt;&amp;2 echo "An unhandled error occurred." &gt;&amp;2 intentionalExit 1 } intentionalExit () { trap - EXIT # Unregister the EXIT trap exit $1 } trap errorExit EXIT # Trap script errors var_scriptfilename="$(basename "$0")" # ==== START OF TEST ==== var_counter=0 ((var_counter++)) echo "var_counter is $var_counter" &gt;&amp;2 # ===== END OF TEST ===== intentionalExit 0 </code></pre> <p>If I run it in Cygwin's bash it produces the intended output:</p> <pre><code>var_counter is 1 </code></pre> <p>However, if I run it on my Debian Squeeze box, which is its intended destination, I end up in the EXIT trap:</p> <pre><code>ERROR (test.increment.sh): An unhandled error occurred. </code></pre> <p>...Why is that?</p> <p>If I remove the -e option it works as expected on both systems, but I want to keep -e in use, obviously.</p> <p>The slightly more cumbersome "universal" variant, <code>var_counter=$(($var_counter+1))</code>, works with -e being set on both shells, but I would prefer to use the first notation (or something similar-looking) since it clearly sticks out as an increment operation when reading the code.</p> <p><code>bash --version</code> on the Cygwin bash says:</p> <pre><code>GNU bash, version 3.2.51(24)-release (i686-pc-cygwin) Copyright (C) 2007 Free Software Foundation, Inc. </code></pre> <p>On Debian, it is:</p> <pre><code>GNU bash, Version 4.1.5(1)-release (x86_64-pc-linux-gnu) Copyright (C) 2009 Free Software Foundation, Inc. </code></pre> <p>I am intrigued as to why this is that way. Does anybody know the cause of this behavior?</p> <p>Also, does anybody know of a similar-looking way to increment a variable in bash that I could use?</p>
 

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