Stream: helpdesk (published)

Topic: ✔ Alternative to `sprint`

Sergio Vargas (Apr 02 2024 at 23:30):

I need to write to an external program and read its output, as an array of bytes.

I could do:

input_data = "foo bar"
cout = IOBuffer()
open(`cat`, "w", cout) do cin
    write(cin, input_data)
end
output = take!(cout)

Or I could do:

output = sprint() do cout
    open(`cat`, "w", cout) do cin
        write(cin, input_data)
    end
end

Is there a function like sprint that returns the bytes like take! does? Or better yet, is there a function that I can just call like output = f(`cmd`, input_data)?

jar (Apr 02 2024 at 23:59):

julia> read(`date -u`)
32-element Vector{UInt8}:
 0x54
 0x75
 0x65
 0x20

Sergio Vargas (Apr 03 2024 at 00:24):

That works if the command doesn't read anything, but if I try to write something to its stdin, I don't get anything back:

julia> cin = IOBuffer();

julia> write(cin, "foo bar")
7

julia> read(pipeline(`cat`; stdin=cin))
UInt8[]

Gunnar Farnebäck (Apr 03 2024 at 05:47):

julia> read(pipeline(IOBuffer("foo bar"), `cat`), String)
"foo bar"

Gunnar Farnebäck (Apr 03 2024 at 05:51):

Btw, a seekstart(cin) in your previous example had accomplished the same thing.

Notification Bot (Apr 03 2024 at 15:22):

Sergio Vargas has marked this topic as resolved.

Sergio Vargas (Apr 03 2024 at 15:28):

Thanks @Gunnar Farnebäck . Neither the docs nor the posts I had read on discourse showed that you could simply pass the IOBuffer as an argument. That's much more convenient than the stdio kwargs.

Gunnar Farnebäck (Apr 03 2024 at 17:39):

The pipeline docstring has some hints:

pipeline(from, to) is equivalent to pipeline(from, stdout=to) when from
is a command, and to pipeline(to, stdin=from) when from is another kind of data
source.

Last updated: Dec 28 2024 at 04:38 UTC