bash: using subshells

x.sh

% time for ((i=0; i < 1000; i++)); do \bash -c ':;:' ; done

real    0m4.710s
user    0m0.444s
sys 0m1.420s

% time for ((i=0; i < 1000; i++)); do \dash -c ':;:' ; done

real    0m3.047s
user    0m0.080s
sys 0m0.964s

% time for ((i=0; i < 1000; i++)); do (:;:) ; done

real    0m3.057s
user    0m0.076s
sys 0m0.944s

% foo () (:;:)
% time for ((i=0; i < 1000; i++)); do foo ; done

real    0m2.727s
user    0m0.220s
sys 0m0.696s

% time for ((i=0; i < 1000; i++)); do :|{ :;:; } ; done

real    0m4.022s
user    0m0.100s
sys 0m1.436s

% time for ((i=0; i < 1000; i++)); do :|(:;:) ; done

real    0m4.041s
user    0m0.192s
sys 0m1.352s 

% time for ((i=0; i < 1000; i++)); do _=$(:;:) ; done

real    0m2.588s
user    0m0.136s
sys 0m0.956s

% time for ((i=0; i < 1000; i++)); do { _=$(:;:); } ; done

real    0m2.540s
user    0m0.148s
sys 0m0.936s

% time for ((i=0; i < 1000; i++)); do ( _=$(:;:) ) ; done

real    0m5.705s
user    0m0.116s
sys 0m0.888s

% time for ((i=0; i < 1000; i++)); do : $(:;:) ; done

real    0m2.559s
user    0m0.256s
sys 0m0.844s

% time for ((i=0; i < 1000; i++)); do <<< $(:;:) ; done

real    0m2.732s
user    0m0.156s
sys 0m1.104s

% time for ((i=0; i < 1000; i++)); do : <(:;:) ; done

real    0m1.077s
user    0m0.052s
sys 0m0.916s

% time for ((i=0; i < 1000; i++)); do <<< <(:;:) ; done

real    0m1.144s
user    0m0.120s
sys 0m1.008s

% time for ((i=0; i < 1000; i++)); do _=<(:;:) ; done

real    0m0.852s
user    0m0.104s
sys 0m0.628s

% time { for ((i=0; i < 1000; i++)); do { :;:; } & done; wait; }

real    0m1.158s
user    0m0.092s
sys 0m0.676s

@ % time { for ((i=0; i < 1000; i++)); do _=<(\ls -d / 1>&3) ; done; } 3>&1 | wc -l
1000

real    0m2.315s
user    0m0.128s
sys 0m0.748s
*@ % time { for ((i=0; i < 1000; i++)); do : <(\ls -d / 1>&3) ; done; } 3>&1 | wc -l
1000

real    0m2.325s
user    0m0.140s
sys 0m0.736s

% time { for ((i=0; i < 1000; i++)); do <<< <(\ls -d / 1>&3) ; done; } 3>&1 | wc -l
1000

real    0m2.421s
user    0m0.144s
sys 0m0.860s

*@ % time { for ((i=0; i < 1000; i++)); do _=$(\ls -d / 1>&3) ; done; } 3>&1 | wc -l
1000

real    0m5.530s
user    0m0.196s
sys 0m0.796s