Eight ways to speed up your shell scripts

        Few of the tips to speed up the execution of your shell scripts
 

$ f() { echo -n }; time for i in {0..100}; do v=$( f ); done

real    0m4.189s
user    0m0.000s
sys     0m4.188s

$ f() { _F="" }; time for i in {0..100}; do f; v=$_F; done

real    0m0.006s
user    0m0.000s
sys     0m0.000s

I found a few other equivalent operations which can be used to speed up shell scripts to varying degrees (none like the above) depending on the task at hand.  As Chris says, “the extra few milliseconds … may not seem significant, but scripts often loop hundred of even thousands of times.”

${#array[@]} is faster than () when expanding an array (#7)

$ a=(); time for i in {0..1000}; do a=(${a[@]} $i);done; echo ${#a[@]}

real    0m3.545s
user    0m3.544s
sys     0m0.000s
1001

$ a=(); time for i in {0..1000}; do a[${#a[@]}]=$i;done; echo ${#a[@]}

real    0m0.043s
user    0m0.040s
sys     0m0.003s
1001

< is faster than cat

$ time for i in {0..10000}; do var=`cat out`;done

real    0m9.328s
user    0m2.892s
sys     0m6.436s

$ time for i in {0..10000}; do var=`<out`;done

real    0m5.930s
user    0m1.412s
sys     0m4.520s

echo is faster than printf (though not nearly as powerful)

$ time for i in {0..100000}; do printf "\n"; done >/dev/null

real    0m4.446s
user    0m4.076s
sys     0m0.236s

$ time for i in {0..100000}; do echo; done >/dev/null

real    0m3.291s
user    0m3.100s
sys     0m0.184s 
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