# -*- awk -*-

# hello world
# print a simple string on stdout
BEGIN { 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)
BEGIN { print ARGV[1] }

# env
# access environment variable
BEGIN { print ENVIRON["HOME"] }

# test file exists
# return exit code error (non zero) if a file does not exist
BEGIN { if (system("[ -e /etc/mtab ]")) exit 1 }

# test file readable
# return exit code error (non zero) if a file is not readable
BEGIN { if (system("[ -r /etc/mtab ]")) exit 1 }

# formatting
# print integers in a simple formatted string
BEGIN { a=1; b=2; print a " + " b " = " a + b }

# system
# call an external program and check the return value
BEGIN { 
  if (system("false")) print "false failed" > "/dev/stderr" 
  system("echo done")
}


# sed in place
# remove #-comments from a file (modifying the file, i.e. in place)
BEGIN { 
  if (!("mktemp /tmp/sed.XXXXXX" | getline tmp)) exit 1
}
{ sub("#.*", ""); print >> tmp }
END {
  system("cp -f " tmp " " ARGV[1])
  system("rm -f " tmp)
}


# compile what must be
# find and compile .c files into .o when the .o is old or absent
BEGIN { 
  while ("find -name '*.c'" | getline) {
    c = $0
    sub(/.c$/, ".o")
    if (system(sprintf("[ %s -nt %s ]", c, $0)) == 0) {
      print "compiling", c, "to", $0
      system(sprintf("gcc -c -o '%s' '%s'", $0, c))
    }
  }    
}


# grep
# grep with -F -i -h handling, usage, grep'ing many files
function usage() {
  print "usage: grep [-F] [-i] regexp [files...]" > "/dev/stderr"
  exit 1
}

BEGIN {
  for (i = 1; i < ARGC; i++) {
    s = ARGV[i]
    ARGV[i] = ""
         if (s == "-h") usage()
    else if (s == "-i") IGNORECASE = 1
    else if (s == "-F") F = 1
    else break
  }
  if (i == ARGC) usage()
  re = s
  prefix = i + 2 < ARGC
}

{
  if (F ? index($0, re) : match($0, re))
    print (prefix ? (FILENAME ":") : "") $0
}