pgrep: optimize length detection

When calculating the length, the ^$ character needs to be removed if the -x parameter is present.

Closes: #635

Author: Franklin-Qi

src/uu/pgrep/src/process_matcher.rs

@@ -151,8 +151,20 @@ pub fn get_match_settings(matches: &ArgMatches) -> UResult<Settings> {
 pub fn find_matching_pids(settings: &Settings) -> UResult<Vec<ProcessInformation>> {
     let mut pids = collect_matched_pids(settings)?;
 
+    let is_long_match = if settings.exact {
+        settings
+            .regex
+            .as_str()
+            .trim_matches('^')
+            .trim_matches('$')
+            .len()
+            > 15
+    } else {
+        settings.regex.as_str().len() > 15
+    };
+
     if pids.is_empty() {
-        if !settings.full && settings.regex.as_str().len() > 15 {
+        if !settings.full && is_long_match {
             let msg = format!("pattern that searches for process name longer than 15 characters will result in zero matches\n\
                             Try `{} -f' option to match against the complete command line.", uucore::util_name());
             return Err(USimpleError::new(1, msg));

tests/by-util/test_pgrep.rs

@@ -654,7 +654,6 @@ fn test_pidfile_fcntl_locked() {
 
     // spawn a flock process that locks the file
     let mut flock_process = Command::new("flock")
-        .arg("--fcntl")
         .arg(temp_file.path())
         .arg("sleep")
         .arg("2")
@@ -718,3 +717,31 @@ fn test_env_multiple_filters() {
     // Multiple filters use OR logic
     new_ucmd!().arg("--env=PATH,NONEXISTENT").succeeds();
 }
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_exact_long_pattern_no_match() {
+    new_ucmd!()
+        .arg("-x")
+        .arg("12345678901234")
+        .fails()
+        .code_is(1);
+}
+
+#[test]
+fn test_pattern_longer_than_15_characters() {
+    new_ucmd!()
+        .arg("1234567890123456")
+        .fails()
+        .code_is(1)
+        .stderr_contains("longer than 15 characters");
+}
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_pool_workqueue_release() {
+    new_ucmd!()
+        .arg("pool_workqueue_release")
+        .succeeds()
+        .stdout_matches(&Regex::new(MULTIPLE_PIDS).unwrap());
+}