Run echo using Sys.command

Learning
1

I am trying to print colored texts in terminal using echo -e ‘\x1b[31mhello world\x1b[0m’. Everything is well in the terminal when I type this myself, but the code below outputs “-e \x1b[31mhello world\x1b[0m” itself. What’s the problem? How can I fix it?

let _ = 
  ignore (Sys.command ("echo -e '\\x1b[31mhello world\\x1b[0m'"))

I am working in ubuntu, WSL2 to be exact.

2

Properly using Sys.command needs quoting technology you likely don’t want to know about.

Is there any strong reason for you not to use Unix.create_process or simply print_endline ? In these cases WYSYWG.

1 Like
3

You need to stop quoting the backslash:

let _ = 
  ignore (Sys.command ("echo -e '\x1b[31mhello world\x1b[0m'"))

Ditto.

Cheers,
Nicolas

4

Heh indeed. It is for this very reason that the helper scripts I wrote for camlp5 and pa_ppx that need to do all sorts of shell-quoting … are written in Perl, and not in OCaml. I simply didn’t want to figure out all the quoting b.s., and it wasn’t relevant to the goals of the actual code being implemented.

If I had to do this, I’d sooner learn how to use terminfo (or termcap, or ncurses) from OCaml, than try to use the shell.

5

Filename.quote_command … Lest we reinvent the wheel.