When dealing with a string, an external program is many, many times slower than using shell internals.

Code:

$ x=123.456
$ time echo "${x%.*}"
123

real    0m0.000s
user    0m0.000s
sys     0m0.000s
$ time echo "$x" | awk -F. '{print $1}'
123

real    0m0.045s
user    0m0.002s
sys     0m0.001s
$ time echo "$x" | sed 's/\(.*\)\..*/\1/'
123

real    0m0.048s
user    0m0.000s
sys     0m0.004s

In the time it take to create the new process, a hundred (give or take) lines of shell code can be executed.

I have an 80-line shell function, fpmul, which multiplies floating point numbers.

Code:

$ time fpmul 12.34 56.78 90.12
63143.947824

real    0m0.000s
user    0m0.000s
sys     0m0.001s

Awk is much slower:

Code:

$ time awk 'BEGIN { print 12.34 * 56.78 * 90.12; exit }'
63143.9

real    0m0.033s
user    0m0.000s
sys     0m0.001s

That is exactly when a more efficient use of the shell is important.

On the contrary, complicated programs can be written in the shell that perform faster than those using another language.

There are times when an external program is better, especially dealing with large files.

Calling an external command to deal with a single string is the most inefficient code possible.

Write for the POSIX shell and there are no compatibility issues.

Write for bash or ksh when extra efficiency is needed for specific tasks.

Since most people will have some familiarity with the shell, it is faster to learn to use it well than to learn a new programming language.