为什么有人会使用echo为bash或ksh中的变量赋值？

Question

Recently I came across an unusual use of echo to assign variables in a client's ksh scripts.

For example, there are many instances such as the following

a='something'
b='else'
c=`echo "${a} ${b}"`

I have been unable to come up with any reason why someone may have done this.

Could there be some legacy reason for this? (I've been doing shell for 30+ years, and never before have I seen this)

Or is it just ignorance?

Answer 1

There is no compelling reason whatsoever for this, either in current bash, or its POSIX sh or Bourne predecessors.

c="$a $b"

...is a complete replacement for the code given, and runs far faster (try putting it in a loop; command substitutions, as created by backticks, fork off a new shell as a subprocess and read its stdout -- a high-overhead operation).

Answer 2

What you saw is an example of bad use of echo because c could be declared as:

c="$a $b"

A common use of echo is when you need comands to filter output, for example

$ line="100090 $100,00 Mary"
$ name=`echo "$line" | grep -Eo "[a-zA-Z]+$"`
echo $name
Mary

But it would be more efficient if you don't use echo at all. The same thing above can be done with "read", without creating a new process:

$ line="100090 $100,00 Paul"
$ read -r _ _ name _ <<<"$line"
echo $name
Paul