ls: Allow reading time-style from TIME_STYLE environment variable

According to GNU manual.

Author: drinkcat

src/uu/ls/src/ls.rs

@@ -266,7 +266,11 @@ fn parse_time_style(options: &clap::ArgMatches) -> Result<(String, Option<String
         Ok((recent.to_string(), older.map(String::from)))
     }
 
-    if let Some(field) = options.get_one::<String>(options::TIME_STYLE) {
+    if let Some(field) = options
+        .get_one::<String>(options::TIME_STYLE)
+        .map(|s| s.to_owned())
+        .or_else(|| std::env::var("TIME_STYLE").ok())
+    {
         //If both FULL_TIME and TIME_STYLE are present
         //The one added last is dominant
         if options.get_flag(options::FULL_TIME)
@@ -287,7 +291,7 @@ fn parse_time_style(options: &clap::ArgMatches) -> Result<(String, Option<String
                 }
                 field
             } else {
-                field
+                &field
             };
 
             match time_styles.get(field) {

tests/by-util/test_ls.rs

@@ -2068,6 +2068,23 @@ fn test_ls_styles() {
         .arg("-x")
         .succeeds()
         .stdout_is("test  test2\n");
+
+    // Time style can also be setup from environment
+    scene
+        .ucmd()
+        .env("TIME_STYLE", "full-iso")
+        .arg("-l")
+        .succeeds()
+        .stdout_matches(&re_full);
+
+    // ... but option takes precedence
+    scene
+        .ucmd()
+        .env("TIME_STYLE", "full-iso")
+        .arg("-l")
+        .arg("--time-style=long-iso")
+        .succeeds()
+        .stdout_matches(&re_long);
 }
 
 #[test]