newOS4: tail -n/-N flags + live follow mode (-f) with test harness

1 files changed, 45 insertions, 4 deletions

diff --git a/modules/core/module-fs.js b/modules/core/module-fs.js
index 25442eb..2fb9e65 100644
--- a/modules/core/module-fs.js
+++ b/modules/core/module-fs.js
@@ -232,11 +232,52 @@ class FileSystemModule {
             this.terminal.print(c.split('\n').slice(0, n).join('\n'));
         };
         this.commands['tail'] = (args) => {
-            if(!args[0]) return this.terminal.print('Usage: tail <filename> [lines]', 'warning');
-            const c = this.terminal.fs.readFile(args[0]);
-            if(c === null || c === undefined) return this.terminal.print('tail: ' + args[0] + ': No such file', 'error');
-            const n = args[1] ? parseInt(args[1]) : 10;
+            const self = this;
+            let follow = false, n = 10;
+            const positional = [];
+            for (let i = 0; i < (args || []).length; i++) {
+                const a = args[i];
+                if (a === '-f' || a === '--follow') follow = true;
+                else if (a === '-n') {
+                    const v = args[++i];
+                    if (v === undefined || !/^\d+$/.test(v)) return this.terminal.print('tail: -n requires a number', 'error');
+                    n = parseInt(v, 10);
+                }
+                else if (/^-\d+$/.test(a)) n = parseInt(a.slice(1), 10);
+                else if (a === '-c' || a === '-q' || a === '-v' || a === '--pid') return this.terminal.print('tail: option ' + a + ' not supported', 'error');
+                else if (a.startsWith('-')) return this.terminal.print('tail: invalid option: ' + a, 'error');
+                else positional.push(a);
+            }
+            const file = positional[0];
+            if (!file) return this.terminal.print('Usage: tail [-f] [-n N] <file> — last N lines; -f follows changes (Ctrl+C or Esc to stop)', 'warning');
+            if (positional[1] && /^\d+$/.test(positional[1])) n = parseInt(positional[1], 10); // legacy back-compat: tail <file> <count>
+            const c = this.terminal.fs.readFile(file);
+            if (c === null || c === undefined) return this.terminal.print('tail: ' + file + ': No such file', 'error');
             this.terminal.print(c.split('\n').slice(-n).join('\n'));
+            if (!follow) return;
+            // stop any previous follow before starting a new one
+            if (this.terminal._activeFollow && this.terminal._activeFollow.interval) clearInterval(this.terminal._activeFollow.interval);
+            this.terminal._activeFollow = null;
+            let offset = c.length;
+            const interval = setInterval(() => {
+                const cur = self.terminal.fs.readFile(file);
+                if (cur === null || cur === undefined) {
+                    self.terminal.stopFollow('tail: ' + file + ': file removed — follow stopped');
+                    return;
+                }
+                if (cur.length < offset) {
+                    self.terminal.print('tail: ' + file + ': file truncated — following from start', 'warning');
+                    self.terminal.print(cur);
+                    offset = cur.length;
+                    return;
+                }
+                if (cur.length > offset) {
+                    self.terminal.print(cur.slice(offset));
+                    offset = cur.length;
+                }
+            }, 1500);
+            this.terminal._activeFollow = { interval, file };
+            this.terminal.print('tail: following ' + file + ' (Ctrl+C or Esc to stop)', 'text-muted');
         };
         this.commands['sort'] = (args) => {
             if(!args[0]) return this.terminal.print('Usage: sort <filename>', 'warning');