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+## 'time' is undefined for compound commands, time sh -c instead.
+
+### Problematic code:
+
+```sh
+time for i in *.bmp; do convert "$i" "$i.png"; done
+```
+
+### Correct code:
+
+```sh
+time sh -c 'for i in *.bmp; do convert "$i" "$i.png"; done'
+```
+### Rationale:
+
+`time` is only defined for Simple Commands [by POSIX](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/time.html). Timing loops, command groups and similar is not.
+
+### Exceptions:
+
+None. If you use a shell that supports this (e.g. bash, ksh), specify this shell in the shebang.
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