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--- bash:arithmetic_evaluation_and_errexit_trap [2016/11/25 16:07] – created peter
+++ bash:arithmetic_evaluation_and_errexit_trap [2021/01/26 12:00] (current) – removed peter
@@ Line 1: / Line 1: @@
-====== Bash - Arithmetic evaluation and errexit trap ======
-<code bash>
-count=0
-things="0 1 0 0 1"
-for i in $things;
-do
-   if [ $i == "1" ]; then
-       (( count++ ))
-   fi
-done
-echo "Count is ${count}"
-</code>
-Looks fine? I've probably written this many times. There's a small gotcha:
-<WRAP box>
-((expression))
-The expression is evaluated according to the rules described below under ARITHMETIC EVALUATION. If the value of the expression is non-zero, the return status is 0; otherwise the return status is 1. This is exactly equivalent to let "expression".
-</WRAP>
-When you run this script with -e or enable errexit -- probably because the script has become too big to be reliable without it -- count++ is going to return 0 (post-increment) and per above stop the script. A definite trap to watch out for!