FAQ entry on shell metacharacters in run (#43633)

Author: stevengj

doc/src/manual/faq.md

@@ -141,6 +141,25 @@ parsing the file once it reaches to the `exec` statement.
     ```
     instead. Note that with this strategy [`PROGRAM_FILE`](@ref) will not be set.
 
+### Why doesn't `run` support `*` or pipes for scripting external programs?
+
+Julia's [`run`](@ref) function launches external programs *directly*, without
+invoking an [operating-system shell](https://en.wikipedia.org/wiki/Shell_(computing))
+(unlike the `system("...")` function in other languages like Python, R, or C).
+That means that `run` does not perform wildcard expansion of `*` (["globbing"](https://en.wikipedia.org/wiki/Glob_(programming))),
+nor does it interpret [shell pipelines](https://en.wikipedia.org/wiki/Pipeline_(Unix)) like `|` or `>`.
+
+You can still do globbing and pipelines using Julia features, however.  For example, the built-in
+[`pipeline`](@ref) function allows you to chain external programs and files, similar to shell pipes, and
+the [Glob.jl package](https://github.com/vtjnash/Glob.jl) implements POSIX-compatible globbing.
+
+You can, of course, run programs through the shell by explicitly passing a shell and a command string to `run`,
+e.g. ```run(`sh -c "ls > files.txt"`)``` to use the Unix [Bourne shell](https://en.wikipedia.org/wiki/Bourne_shell),
+but you should generally prefer pure-Julia scripting like ```run(pipeline(`ls`, "files.txt"))```.
+The reason why we avoid the shell by default is that [shelling out sucks](https://julialang.org/blog/2012/03/shelling-out-sucks/):
+launching processes via the shell is slow, fragile to quoting of special characters,  has poor error handling, and is
+problematic for portability.  (The Python developers came to a [similar conclusion](https://www.python.org/dev/peps/pep-0324/#motivation).)
+
 ## Functions
 
 ### I passed an argument `x` to a function, modified it inside that function, but on the outside, the variable `x` is still unchanged. Why?