Add tail utility

tail.nim

@@ -0,0 +1,29 @@
+import cligen, os, math, deques
+import common
+
+proc main(files:seq[string], lines=10, bytes=0, quiet=false) =
+#    if files.len == 0:
+#        files.add "-"
+    for file in files:
+        if files.len > 1 and not quiet:
+            writeLine(stdout, "==> " & (if file == "-": "standard input" else: file) & " <==")
+        var f = if file == "-": stdin
+                else: open(file, fmRead)
+        if bytes > 0:
+            var q = initDeque[char]()
+            while not f.endOfFile:
+                if q.len > bytes:
+                    q.popFirst
+                q.addLast(f.readChar)
+            for item in q.items:
+                write(stdout, item)
+        elif lines > 0:
+            var q = initDeque[string]()
+            for line in lines(f):
+                if q.len > lines:
+                    q.popFirst
+                q.addLast line
+            for line in q.items:
+                writeLine(stdout, line)
+
+dispatch(main, version=("version", nimbaseVersion))