I've seen a lot of answers and comments on Stack Overflow that mention doing something to avoid a subshell. In some cases, a functional reason for this is given (most often, the potential need to read a variable outside the subshell that was assigned inside it), but in other cases, the avoidance seems to be viewed as an end in itself. For example
union of two columns of a tsv file
suggesting { ... ; } | ... rather than
( ... ) | ..., so there's a subshell either way.
Linux bash script to copy files
explicitly stating,
"the goal is just to avoid a subshell"
Why is this? Is it for style/elegance/beauty? For performance (avoiding a fork)? For preventing likely bugs? Something else?
There are a few things going on.
First, forking a subshell might be unnoticible when it happens only once, but if you do it in a loop, it adds up to measurable performance impact. The performance impact is also greater on platforms such as Windows where forking is not as cheap as it is on modern Unixlikes.
Second, forking a subshell means you have more than one context, and information is lost in switching between them -- if you change your code to set a variable in a subshell, that variable is lost when the subshell exits. Thus, the more your code has subshells in it, the more careful you have to be when modifying it later to be sure that any state changes you make will actually persist.
See BashFAQ #24 for some examples of surprising behavior caused by subshells.