Add tac utility

nimbase.nimble

@@ -8,6 +8,6 @@ requires      "nim >= 0.19.0"
 requires      "cligen >= 0.9.19"
 requires      "stint >= 0.0.1"
 
-bin           = @["add", "cat", "cp", "div", "echo", "factor", "false", "head", "mkdir", "mul", "nl", "pwd", "rm", "seq", "shuf", "sleep", "sub", "tee", "touch", "true", "yes"]
+bin           = @["add", "cat", "cp", "div", "echo", "factor", "false", "head", "mkdir", "mul", "nl", "pwd", "rm", "seq", "shuf", "sleep", "sub", "tac", "tee", "touch", "true", "yes"]
 
 binDir        = "bin"

nl.nim

@@ -1,11 +1,26 @@
 import cligen
 import common
 
-proc main(files:seq[string], lineIncrement=1) =
-    for file in files:
+proc digits(num:int): int =
+    result = 1
+    var x = num
+    while x div 10 >= 1:
+        inc result
+        x = x div 10
+
+proc spaces(num:int): string =
+    for i in 1..num:
+        result &= " "
+
+proc formatNumber(num:int, width:int): string =
+    result = if digits(num) > width: $num
+             else: spaces(width - digits(num)) & $num
+
+proc main(files:seq[string], lineIncrement=1, numberSeparator="\t", numberWidth=6) =
     var lineNr = 0
+    for file in files:
         for line in lines(file):
             lineNr += lineIncrement
-            writeLine(stdout, $(lineNr) & line)
+            writeLine(stdout, formatNumber(lineNr, numberWidth) & numberSeparator & line)
 
 dispatch(main, version=("version", nimbaseVersion))

tac.nim

@@ -0,0 +1,34 @@
+import cligen, os, streams
+import common
+
+proc catFile(file:string) =
+    if not existsFile(file):
+        err "tac: " & file & ": No such file or directory"
+        system.quit 1
+    var
+        f = open(file, fmRead)
+        reverseLines: seq[string]
+    for line in lines(f):
+        reverseLines = line & reverseLines
+    for line in reverseLines:
+        writeLine(stdout, line)
+
+proc catStdin() =
+    var
+        line = ""
+        reverseLines: seq[string]
+    while stdin.readLine(line):
+        reverseLines = line & reverseLines
+    for line in reverseLines:
+        writeLine(stdout, line)
+
+proc main(files:seq[string]) =
+    if files.len == 0:
+        catStdin()
+    for file in files:
+        if file == "-":
+            catStdin()
+        else:
+            catFile(file)
+
+dispatch(main, version=("version", nimbaseVersion))