(docs) Cookbooks "Run an External Command and Process Stdout" and "Run Piped External Commands"

data/cookbook/run-command-process-stdout/00-stdlib.ml

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+---
+packages: []
+---
+
+(*
+  The function `Unix.open_process_in` runs the given command in parallel with the program.
+  The standard output of the command is redirected to a pipe, which can be read via the returned input channel.
+*)
+let run cmd =
+  let inp = Unix.open_process_in cmd in
+  let r = In_channel.input_all inp in
+  In_channel.close inp; r
+
+(* We call the `ps` command with argument `-x` on the POSIX shell and print its standard output. *)
+let () =
+  let ps_output = run "ps -x" in
+  ps_output
+  |> print_endline

data/cookbook/run-command-process-stdout/01-feather.ml

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+---
+packages:
+- name: feather
+  tested_version: 0.3.0
+  used_libraries:
+  - feather
+---
+
+(* `Feather.process` executes a program and `Feather.collect` returns a single string containing the whole standard output. *)
+let () =
+  let ps_output =
+    Feather.(process "ps" ["-x"]
+    |> collect stdout)
+  in
+  print_endline ps_output

data/cookbook/run-command-process-stdout/02-shexp.ml

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+---
+packages:
+- name: shexp
+  tested_version: v0.16.0
+  used_libraries:
+  - shexp
+  - shexp.process
+---
+(* The module Shexp_process.Infix contains the `|-` (pipe) operator. *)
+open Shexp_process.Infix
+
+(* We use the pipe operator to build a sequence consisting of the single command
+  `ps -x`, then `read_all` to obtain its standard output. *)
+let () =
+  let ps_output =
+    let open Shexp_process in
+      eval (run "ps" ["-x"] |- read_all)
+  in
+  print_endline ps_output

data/cookbook/run-piped-commands/01-feather.ml

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+---
+packages:
+- name: feather
+  tested_version: 0.3.0
+  used_libraries:
+  - feather
+---
+
+(* The `|.` operator from the `Feather` module can be used to pipe different commands. *)
+let () =
+  let sort_output =
+    Feather.(echo "t\nz\nu\na\nb" |. process "sort" [""] |> collect stdout)
+  in
+  print_string sort_output

data/cookbook/run-piped-commands/02-shexp.ml

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+---
+packages:
+- name: shexp
+  tested_version: v0.16.0
+  used_libraries:
+  - shexp
+  - shexp.process
+---
+(* The module Shexp_process.Infix contains the `|-` (pipe) operator. *)
+open Shexp_process.Infix
+
+(* We use the pipe operator and build a sequence of commands, then `read_all` to obtain its standard output. *)
+let () =
+  let sort_output =
+    let open Shexp_process in
+      eval (
+        run "echo" ["t\nz\nu\na\nb"]
+        |- run "sort" []
+        |- read_all)
+  in
+  print_string sort_output