optionally pipe contents of variable to stdin of an exec command

Cargo.toml

@@ -26,6 +26,7 @@ lazy_static = "1.4.0"
 num_cpus = "1.13.0"
 rand = "0.8.5"
 hdrhistogram = "7.4.0"
+tempfile = "3.10.1"
 
 # Add openssl-sys as a direct dependency so it can be cross compiled to
 # x86_64-unknown-linux-musl using the "vendored" feature below

src/actions/exec.rs

@@ -1,7 +1,9 @@
 use async_trait::async_trait;
 use colored::*;
 use serde_json::json;
-use std::process::Command;
+use std::io::{Seek, SeekFrom, Write};
+use std::process::{Command, Stdio};
+use tempfile::tempfile;
 use yaml_rust::Yaml;
 
 use crate::actions::Runnable;
@@ -15,6 +17,7 @@ pub struct Exec {
   name: String,
   command: String,
   pub assign: Option<String>,
+  pub stdin: Option<String>,
 }
 
 impl Exec {
@@ -26,11 +29,13 @@ impl Exec {
     let name = extract(item, "name");
     let command = extract(&item["exec"], "command");
     let assign = extract_optional(item, "assign");
+    let stdin = extract_optional(item, "stdin");
 
     Exec {
       name,
       command,
       assign,
+      stdin,
     }
   }
 }
@@ -46,7 +51,23 @@ impl Runnable for Exec {
 
     let args = vec!["bash", "-c", "--", final_command.as_str()];
 
-    let execution = Command::new(args[0]).args(&args[1..]).output().expect("Couldn't run it");
+    let mut file_for_stdin = Stdio::null();
+
+    if let Some(ref key) = self.stdin {
+      let interpolator = interpolator::Interpolator::new(context);
+      let eval = format!("{{{{ {} }}}}", key);
+      let cmd_input = interpolator.resolve(&eval, true);
+      let mut f = tempfile().unwrap();
+      if let Err(why) = f.write_all(cmd_input.as_bytes()) {
+        panic!("couldn't write {}: {}", key, why);
+      }
+      if let Err(why) = f.seek(SeekFrom::Start(0)) {
+        panic!("couldn't rewind file: {}: {}", key, why);
+      }
+      file_for_stdin = Stdio::from(f);
+    }
+
+    let execution = Command::new(args[0]).args(&args[1..]).stdin(file_for_stdin).output().expect("Couldn't run it");
 
     let output: String = String::from_utf8_lossy(&execution.stdout).into();
     let output = output.trim_end().to_string();