Merge pull request #21197 from stevengj/cmdarray

access Cmd elements as an array of strings

base/process.jl

@@ -824,3 +824,11 @@ wait(x::Process)      = if !process_exited(x); stream_wait(x, x.exitnotify); end
 wait(x::ProcessChain) = for p in x.processes; wait(p); end
 
 show(io::IO, p::Process) = print(io, "Process(", p.cmd, ", ", process_status(p), ")")
+
+# allow the elements of the Cmd to be accessed as an array or iterator
+for f in (:length, :endof, :start, :eachindex, :eltype, :first, :last)
+    @eval $f(cmd::Cmd) = $f(cmd.exec)
+end
+for f in (:next, :done, :getindex)
+    @eval $f(cmd::Cmd, i) = $f(cmd.exec, i)
+end

doc/src/manual/running-external-programs.md

@@ -60,6 +60,18 @@ julia> open(`less`, "w", STDOUT) do io
 3
 ```
 
+The program name and the individual arguments in a command can be accessed
+and iterated over as if the command were an array of strings:
+```jldoctest
+julia> collect(`echo "foo bar"`)
+2-element Array{String,1}:
+ "echo"
+ "foo bar"
+
+julia> `echo "foo bar"`[2]
+"foo bar"
+```
+
 ## [Interpolation](@id command-interpolation)
 
 Suppose you want to do something a bit more complicated and use the name of a file in the variable

test/spawn.jl

@@ -466,3 +466,14 @@ end
             Base.showerror(io::IO, e::Error19864) = print(io, "correct19864")
             throw(Error19864())'`),
     stderr=catcmd)) == "ERROR: correct19864"
+
+# accessing the command elements as an array or iterator:
+let c = `ls -l "foo bar"`
+    @test collect(c) == ["ls", "-l", "foo bar"]
+    @test first(c) == "ls" == c[1]
+    @test last(c) == "foo bar" == c[3] == c[end]
+    @test c[1:2] == ["ls", "-l"]
+    @test eltype(c) == String
+    @test length(c) == 3
+    @test eachindex(c) == 1:3
+end