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expand here on our globbing example to illustrate some performance characteristics of the shell script interpreter. Comparing the bash and dash interpreters for this example where a process is spawned for each of 30,000 files, shows that dash can fork the wc processes nearly twice as fast as bash

Comparing the base looping speed by not invoking the wc processes, shows that dash's looping is nearly 6 times faster!

$ time bash -c 'for i in *; do echo "$i">/dev/null; done'
real    0m1.715s
user    0m1.459s
sys     0m0.252s


 
$ time dash -c 'for i in *; do echo "$i">/dev/null; done'
real    0m0.375s
user    0m0.169s
sys     0m0.203s

The looping is still relatively slow in either shell as demonstrated previously, so for scalability we should try and use more functional techniques so iteration is performed in compiled processes.

$ time find -type f -print0 | wc -l --files0-from=- | tail -n1
    30000 total
real    0m0.299s
user    0m0.072s
sys     0m0.221s

The above is by far the most efficient solution and illustrates the point well that one should do as little as possible in shell script and aim just to use it to connect the existing logic available in the rich set of utilities available on a UNIX system.

Stolen From This Page

We'll expand here on our globbing example above to illustrate some performance characteristics of the shell script interpreter. Comparing the bash and dash interpreters for this example where a process is spawned for each of 30,000 files, shows that dash can fork the wc processes nearly twice as fast as bash

Comparing the base looping speed by not invoking the wc processes, shows that dash's looping is nearly 6 times faster!

$ time bash -c 'for i in *; do echo "$i">/dev/null; done'
real    0m1.715s
user    0m1.459s
sys     0m0.252s

$ time dash -c 'for i in *; do echo "$i">/dev/null; done'

real    0m0.375s
user    0m0.169s
sys     0m0.203s

The looping is still relatively slow in either shell as demonstrated previously, so for scalability we should try and use more functional techniques so iteration is performed in compiled processes.

$ time find -type f -print0 | wc -l --files0-from=- | tail -n1

    30000 total
real    0m0.299s
user    0m0.072s
sys     0m0.221s

The above is by far the most efficient solution and illustrates the point well that one should do as little as possible in shell script and aim just to use it to connect the existing logic available in the rich set of utilities available on a UNIX system.

Stolen From Common shell script mistakes by Pádraig Brady.

expand here on our globbing example to illustrate some performance characteristics of the shell script interpreter. Comparing the bash and dash interpreters for this example where a process is spawned for each of 30,000 files, shows that dash can fork the wc processes nearly twice as fast as bash

$ time dash -c 'for i in *; do wc -l "$i">/dev/null; done'
real    0m14.440s
user    0m3.753s
sys     0m10.329s



$ time bash -c 'for i in *; do wc -l "$i">/dev/null; done'
real    0m24.251s
user    0m8.660s
sys     0m14.871s

Comparing the base looping speed by not invoking the wc processes, shows that dash's looping is nearly 6 times faster!

$ time bash -c 'for i in *; do echo "$i">/dev/null; done'
real    0m1.715s
user    0m1.459s
sys     0m0.252s



$ time dash -c 'for i in *; do echo "$i">/dev/null; done'
real    0m0.375s
user    0m0.169s
sys     0m0.203s

The looping is still relatively slow in either shell as demonstrated previously, so for scalability we should try and use more functional techniques so iteration is performed in compiled processes.

$ time find -type f -print0 | wc -l --files0-from=- | tail -n1
    30000 total
real    0m0.299s
user    0m0.072s
sys     0m0.221s

The above is by far the most efficient solution and illustrates the point well that one should do as little as possible in shell script and aim just to use it to connect the existing logic available in the rich set of utilities available on a UNIX system.

Stolen From This Page

expand here on our globbing example to illustrate some performance characteristics of the shell script interpreter. Comparing the bash and dash interpreters for this example where a process is spawned for each of 30,000 files, shows that dash can fork the wc processes nearly twice as fast as bash

bash-4.2$ time dash -c 'for i in *; do wc -l "$i"; done>/dev/null'
real    0m1.238s
user    0m0.309s
sys     0m0.815s


bash-4.2$ time bash -c 'for i in *; do wc -l "$i"; done>/dev/null'
real    0m1.422s
user    0m0.349s
sys     0m0.940s

Comparing the base looping speed by not invoking the wc processes, shows that dash's looping is nearly 6 times faster!

$ time bash -c 'for i in *; do echo "$i">/dev/null; done'
real    0m1.715s
user    0m1.459s
sys     0m0.252s



$ time dash -c 'for i in *; do echo "$i">/dev/null; done'
real    0m0.375s
user    0m0.169s
sys     0m0.203s

The looping is still relatively slow in either shell as demonstrated previously, so for scalability we should try and use more functional techniques so iteration is performed in compiled processes.

$ time find -type f -print0 | wc -l --files0-from=- | tail -n1
    30000 total
real    0m0.299s
user    0m0.072s
sys     0m0.221s

The above is by far the most efficient solution and illustrates the point well that one should do as little as possible in shell script and aim just to use it to connect the existing logic available in the rich set of utilities available on a UNIX system.

Stolen From This Page

We'll expand here on our globbing example above to illustrate some performance characteristics of the shell script interpreter. Comparing the bash and dash interpreters for this example where a process is spawned for each of 30,000 files, shows that dash can fork the wc processes nearly twice as fast as bash

$ time dash -c 'for i in *; do wc -l "$i">/dev/null; done'
real    0m14.440s
user    0m3.753s
sys     0m10.329s



$ time bash -c 'for i in *; do wc -l "$i">/dev/null; done'
real    0m24.251s
user    0m8.660s
sys     0m14.871s

Comparing the base looping speed by not invoking the wc processes, shows that dash's looping is nearly 6 times faster!

$ time bash -c 'for i in *; do echo "$i">/dev/null; done'
real    0m1.715s
user    0m1.459s
sys     0m0.252s



$ time dash -c 'for i in *; do echo "$i">/dev/null; done'
real    0m0.375s
user    0m0.169s
sys     0m0.203s

The looping is still relatively slow in either shell as demonstrated previously, so for scalability we should try and use more functional techniques so iteration is performed in compiled processes.

$ time find -type f -print0 | wc -l --files0-from=- | tail -n1
    30000 total
real    0m0.299s
user    0m0.072s
sys     0m0.221s

The above is by far the most efficient solution and illustrates the point well that one should do as little as possible in shell script and aim just to use it to connect the existing logic available in the rich set of utilities available on a UNIX system.

Stolen From This Page

expand here on our globbing example to illustrate some performance characteristics of the shell script interpreter. Comparing the bash and dash interpreters for this example where a process is spawned for each of 30,000 files, shows that dash can fork the wc processes nearly twice as fast as bash

$ time dash -c 'for i in *; do wc -l "$i">/dev/null; done'
real    0m14.440s
user    0m3.753s
sys     0m10.329s



$ time bash -c 'for i in *; do wc -l "$i">/dev/null; done'
real    0m24.251s
user    0m8.660s
sys     0m14.871s

Comparing the base looping speed by not invoking the wc processes, shows that dash's looping is nearly 6 times faster!

$ time bash -c 'for i in *; do echo "$i">/dev/null; done'
real    0m1.715s
user    0m1.459s
sys     0m0.252s



$ time dash -c 'for i in *; do echo "$i">/dev/null; done'
real    0m0.375s
user    0m0.169s
sys     0m0.203s

The looping is still relatively slow in either shell as demonstrated previously, so for scalability we should try and use more functional techniques so iteration is performed in compiled processes.

$ time find -type f -print0 | wc -l --files0-from=- | tail -n1
    30000 total
real    0m0.299s
user    0m0.072s
sys     0m0.221s

The above is by far the most efficient solution and illustrates the point well that one should do as little as possible in shell script and aim just to use it to connect the existing logic available in the rich set of utilities available on a UNIX system.

Stolen From This Page