# -*- perl -*-

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

# argv
# access command line parameters (no segmentation fault accepted, nor silent exception, so some languages must explicitly check the presence of the argument)
print "$ARGV[0]\n"

# env
# access environment variable
print "$ENV{HOME}\n"

# test file exists
# return exit code error (non zero) if a file does not exist
-e "/etc/mtab" or exit 1

# test file readable
# return exit code error (non zero) if a file is not readable
-r "/etc/mtab" or exit 1

# formatting
# print integers in a simple formatted string
$a=1; $b=2; print "$a + $b = ", $a + $b, "\n"

# system
# call an external program and check the return value
system "false" and warn "false failed\n"; system "echo done"

# sed in place
# remove #-comments from a file (modifying the file, i.e. in place)
% perl -pi -e "s/#.*//"

# compile what must be
# find and compile .c files into .o when the .o is old or absent
use File::Find;

find({ no_chdir => 1, 
       wanted => sub {
           if (($o = $_) =~ s/\.c$/.o/ 
               && -M $_ <= -M $o) {
               print "compiling $_ to $o\n";
               system qw(gcc -c -o), $o, $_;
           }
} }, '.');


# grep
# grep with -F -i -h handling, usage, grep'ing many files
use Getopt::Std;
getopts('Fih', \%h);

!@ARGV || $h{h} and die "usage: grep [-F] [-i] regexp [files...]\n";

$r = ($h{i} && '(?i)') . shift;
$r = "\Q$r" if $h{F};
$prefix = @ARGV > 1;

while (<>) {
    print $prefix && "$ARGV:", $_ if /$r/o;
}