A simple implementation of `head` in Nimrod

head.nim

import parseopt
from strutils import parseInt
from os import existsFile

const usage = """
head [flags] filename
  -n: number of lines (default 10)
  -h,--help: this help
  -v,--version: version 
"""

proc showUsage(msg: string) =
  if msg != nil: echo("head: ",msg)
  quit(usage,1)
  
proc head(file: string, n: int) =
  if not existsFile(file):  quit("file " & file & " does not exist")
  var
    f = open(file)
    i = 0
  for line in f.lines:
    echo(line)
    i += 1
    if i == n: break
  
proc parseCommands() =
  var
    files: seq[string]
    n = 10
  newSeq(files,0)
  for kind, key, val in getopt():
    case kind
    of cmdArgument:
      files.add(key)
    of cmdLongOption, cmdShortOption:
      case key
      of "help", "h": showUsage(nil)
      of "n": 
        n = parseInt(val)
      of "version", "v":
          echo("1.0")
          return
    of cmdEnd: assert(false) # cannot happen
  if len(files) == 0:
    # no filename has been given, so we show the help:
    showUsage("please supply filename")
  if len(files) == 1:
    head(files[0],n)
  else:
    for f in files:
      echo("----- ",f)
      head(f,n)
  
parseCommands()