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Many shell programmers are in the habit of using calls to external commands
instead of using shell built-in commands (an example of this is a call to
usr/bin/echo instead of using the echo command built into the shell.
This script shows sh_wasted.d tracing a shell script that calls /usr/bin/echo
instead of using the built-in.
# sh_wasted.d -c ./func_waste.sh
Tracing... Hit Ctrl-C to end.
Function A
Function B
Function C
Script duration: 3101631 us
External command elapsed times,
FILE NAME TIME(us)
func_waste.sh sleep 3019573
Wasted command elapsed times,
FILE NAME TIME(us)
func_waste.sh /usr/bin/echo 26510
You can see that the calls to /usr/bin/echo took around 26 thousand
microseconds; time wasted by the shell having to access an external command.
Here we trace the same script, except it uses the shell built-in echo command.
# sh_wasted.d -c ./func_abc.sh
Function A
Tracing... Hit Ctrl-C to end.
Function B
Function C
Script duration: 3032616 us
External command elapsed times,
FILE NAME TIME(us)
func_abc.sh sleep 3012920
Wasted command elapsed times,
FILE NAME TIME(us)
The total time here is less and there are no 'wasted' calls to external
commands.
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