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    This is the right answer, but I would just add that as the interface of these utilities is generally via stdin / stdout anyway, that even if every one of them were also implemented as a built-in routine in bash, it would effectively still need to fork itself and create pipes for each command in a pipeline anyway, so there would be only marginal gains Commented Feb 24, 2017 at 1:32
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    @Chunko Yes. subshells are lighter than fork/exec'ed processes though. Commented Feb 24, 2017 at 2:47
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    @slebetman You are missing my point. Subshells are neither threads nor exec'ed processes, regardless of whether they are running on Linux or not. Subshells are just their parent's clone, created by a fork not followed by exec; fork is nowadays a very lightweight operation compared to exec. Commented Feb 24, 2017 at 8:30
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    I measured busybox nofork builtins as having on the order of 10x less overhead than noexec builtins, which in turn had ~5x less overhead than fork+exec of a separate binary. Definitions as per unix.stackexchange.com/a/274322/29483 It's interesting that busybox doesn't nofork everything, although I know some busybox code is shortened by not cleaning up memory, and just relies on being a short-lived process. Commented Feb 24, 2017 at 9:57
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    @jlliagre: On linux a fork creates a process. The point you're perhaps missing is that on Linux they've optimised processes so much that the developers have determined that there is not further advantage creating anything more lightweight. Basically in linux a process is as lightweight as a thread. Commented Feb 24, 2017 at 12:26