Merge pull request #4 from kesslern/shell-commands

Add arbitrary shell commands (Close #3)

README.md

@@ -6,6 +6,7 @@ Storing dotfiles in git repositories allows them to be shared across multiple co
 
 ## Features
 * Make string substitutions in files according to configured key/value pairs.
+* Use output from arbitrary shell commands in templated dotfiles (e.g. for passwords with GNU Pass).
 * Toggle chunks of files per feature flags.
 * Binary files are copied without templating.
 * File permissions are preserved.
@@ -39,6 +40,12 @@ asdf=aoeu
 ```
 will replace all occurances of `{SUBSTITION ONE}` with `123`, `[font size]` with `19`, and `asdf` with `aoeu`.
 
+#### Arbitrary Shell Commands
+If the `=` separating key/value pairs is immediately proceeded by `SHELL `, dot-templater will run the provided command and use the stdout when templating dotfiles. Providing following line in a config file will substitute any occurrance of `SHELL_COMMAND` with `1234`.
+```
+SHELL_COMMAND=SHELL echo 1234
+```
+
 #### Feature Flags
 Any line in the rules configuration file that does not include a `=` character and is not a comment will enable the feature name that matches the line. Dotfiles can designate togglable features with three octothorpes followed by the feature name. 
 ```

src/lib.rs

@@ -13,6 +13,7 @@ use std::io::Lines;
 use std::io::Read;
 use std::io::Write;
 use std::path::Path;
+use std::process::Command;
 use walkdir::WalkDir;
 
 pub struct Config {
@@ -30,7 +31,7 @@ impl Config {
         for line in lines {
             let line = line?;
 
-            match Config::parse_line(line) {
+            match Config::parse_line(line)? {
                 Some(value) => match value {
                     ConfigValue::Feature(it) => {
                         config.features.push(it);
@@ -46,28 +47,51 @@ impl Config {
         Ok(config)
     }
 
-    fn parse_line(line: String) -> Option<ConfigValue> {
+    fn run_command(command: String) -> Result<String, Box<dyn Error>> {
+        let stdout = Command::new("sh")
+            .arg("-c")
+            .arg(&command)
+            .output()?
+            .stdout;
+
+        return Ok(String::from_utf8(stdout)?.trim().to_owned());
+    }
+
+
+    fn parse_line(line: String) -> Result<Option<ConfigValue>, Box<dyn Error>> {
         let mut line = line.trim().to_string();
 
         if line.is_empty() || line.starts_with("#") {
-            return None;
+            return Ok(None);
         }
 
         match line.chars().position(|c| c == '=') {
             Some(idx) => {
-                let mut var = line.split_off(idx);
-                var.remove(0);
-                return Some(ConfigValue::Substitution {
-                    key: line,
-                    value: var,
-                });
+                let mut value = line.split_off(idx);
+                value.remove(0);
+
+                if value.starts_with("SHELL ") {
+                    let command = value.split_off(6);
+                    let result = &Config::run_command(command)?;
+
+                    return Ok(Some(ConfigValue::Substitution {
+                        key: line,
+                        value: result.to_owned(),
+                    }));
+                } else {
+                    return Ok(Some(ConfigValue::Substitution {
+                        key: line,
+                        value: value,
+                    }));
+                }
             }
             None => {
-                return Some(ConfigValue::Feature(line));
+                return Ok(Some(ConfigValue::Feature(line)));
             }
         }
     }
 
+
     fn template_file(&self, source: &Path, dest: &Path) -> Result<(), Box<dyn Error>> {
         let source = BufReader::new(File::open(source)?);
         let mut dest = File::create(dest)?;

test/dotfiles/template

@@ -4,6 +4,8 @@ Are BASICs really better than dogs?
 
 Weird equals stuff can happen: 4 EQUALS
 
+Test a shell command: SHELL_COMMAND
+
 ### FEATURE1
 this should appear
 ### FEATURE1

test/expected/template

@@ -4,5 +4,7 @@ Are cats really better than dogs?
 
 Weird equals stuff can happen: ====
 
+Test a shell command: 1234
+
 this should appear
     this should appear (test indentation)

test/rules

@@ -11,3 +11,5 @@ EMPTY VARIABLE=
 
 FEATURE1
 # More comments...
+
+SHELL_COMMAND=SHELL echo 1234