# -*- python -*-

# hello world
# print a simple string on stdout
print "Hello World"

# argv
# access command line parameters (no segmentation fault accepted, nor silent exception, so some languages must explicitly check the presence of the argument)
import sys; print sys.argv[1]

# env
# access environment variable
import os; print os.environ["HOME"]

# test file exists
# return exit code error (non zero) if a file does not exist
import os, sys
sys.exit(not os.path.exists("/etc/mtab"))


# test file readable
# return exit code error (non zero) if a file is not readable
import sys
try: open("/etc/mtab")
except: sys.exit(1)


# formatting
# print integers in a simple formatted string
a=1; b=2; print a, '+', b ,'=', a + b

# system
# call an external program and check the return value
import os, sys
if os.system("false"):
    sys.stderr.write("false failed\n")
os.system("echo done")


# sed in place
# remove #-comments from a file (modifying the file, i.e. in place)
import fileinput, re

for s in fileinput.input(inplace = 1):
    print re.sub("#.*", "", s),


# compile what must be
# find and compile .c files into .o when the .o is old or absent
from os import *
from fnmatch import *

for dir, _, files in walk('.'):
    for f in filter(files, '*.c'):
        c = path.join(dir, f)
        o = c[0:-2] + '.o'
        if not path.exists(o) or stat(c)[9] > stat(o)[9]:
            print 'compiling', c, 'to', o
            system("gcc -c -o '%s' '%s'" % (o, c))


# grep
# grep with -F -i -h handling, usage, grep'ing many files
import getopt, sys, fileinput, re

opts, args = getopt.getopt(sys.argv[1:], 'hiF')
opts = [ x[0] for x in opts ]

if not args or '-h' in opts:
    print >> sys.stderr, "usage: grep [-F] [-i] regexp [files...]"
    sys.exit(1)

r, files = args[0], args[1:]

if '-F' in opts:
    r = re.sub("\W", lambda i: "\\" + i.group(0), r)

if '-i' in opts:
    re = re.compile(r, re.I)
else:
    re = re.compile(r)
  
for s in fileinput.input(files):
    prefix = ""
    if len(files) > 1:
        prefix = fileinput.filename() + ":"
    if re.search(s):
        print prefix + s,