Understanding the Unix ‘head’ Command

commandline session

head is a program on Unix and Unix-like operating systems used to display the beginning of a text file or piped data.

$sudo head /var/log/syslog
Jan  5 20:10:05 debian syslogd 1.5.0#6.1: restart.
Jan  5 20:10:05 debian anacron[1056]: Job `cron.daily' terminated
Jan  5 20:10:05 debian anacron[1056]: Normal exit (1 job run)
Jan  5 20:12:14 debian acpid: client connected from 1055[0:0]
Jan  5 20:12:14 debian acpid: 1 client rule loaded
Jan  5 20:12:14 debian acpid: client connected from 1055[0:0]
Jan  5 20:12:14 debian acpid: 1 client rule loaded
Jan  5 20:13:03 debian acpid: client 1055[0:0] has disconnected
Jan  5 20:13:03 debian acpid: client 1055[0:0] has disconnected
Jan  5 20:14:54 debian /usr/sbin/gpm[1239]: *** info [daemon/processrequest.c(42)]:
$sudo head -n 5 /var/log/syslog
Jan  5 20:10:05 debian syslogd 1.5.0#6.1: restart.
Jan  5 20:10:05 debian anacron[1056]: Job `cron.daily' terminated
Jan  5 20:10:05 debian anacron[1056]: Normal exit (1 job run)
Jan  5 20:12:14 debian acpid: client connected from 1055[0:0]
Jan  5 20:12:14 debian acpid: 1 client rule loaded
$sudo head -n 0  /var/log/syslog
$sudo head -n 1  /var/log/syslog
Jan  5 20:10:05 debian syslogd 1.5.0#6.1: restart.
$

Print the first 10 lines of each FILE to standard output.
Part of debian coreutils.

 -n, --lines=[-]NUM
 print the first NUM lines instead of the first 10; with the leading
 '-', print all but the last NUM lines of each file

-c, --bytes=[-]NUM
 print the first NUM bytes of each file; with the leading '-', print 
all but the last NUM bytes of each file
$head  /etc/default/grub
# If you change this file or any /etc/default/grub.d/*.cfg file,
# run 'update-grub' afterwards to update /boot/grub/grub.cfg.
# For full documentation of the options in these files, see:
#   info -f grub -n 'Simple configuration'

GRUB_DEFAULT=0
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR=`( . /etc/os-release && echo ${NAME} )`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video=HDMI-1:1920x1080@84"
GRUB_CMDLINE_LINUX=""
$head  -c 10 /etc/default/grub
# If you c$


-v, --verbose
always print headers giving file names

$head  -v /etc/default/grub
==> /etc/default/grub <==
# If you change this file or any /etc/default/grub.d/*.cfg file,
# run 'update-grub' afterwards to update /boot/grub/grub.cfg.
# For full documentation of the options in these files, see:
#   info -f grub -n 'Simple configuration'

GRUB_DEFAULT=0
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR=`( . /etc/os-release && echo ${NAME} )`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video=HDMI-1:1920x1080@84"
GRUB_CMDLINE_LINUX=""
$

-z, --zero-terminated
 line delimiter is NUL, not newline

The -z option explained

ls -ltr command to sort files by time

$ls
greedy-algorithm-example-coin-change-problem.js
longest-common-substring.js
memoization-top-down-approach.js
solving-knapsack-problem-a-recursive-solution.js
solving-knapsack-problem.js
tabulation-bottom-up-approach.js
$
ls  shows the contents  of  the  current  directory


$ls -ltr
total 24
-rw-rw-r-- 1 jeffrin jeffrin  591 Feb  9 21:37 memoization-top-down-approach.js
-rw-rw-r-- 1 jeffrin jeffrin  436 Feb  9 21:56 tabulation-bottom-up-approach.js
-rw-rw-r-- 1 jeffrin jeffrin 2133 Feb 16 22:13 longest-common-substring.js
-rw-rw-r-- 1 jeffrin jeffrin 2288 Feb 18 21:54 solving-knapsack-problem.js
-rw-rw-r-- 1 jeffrin jeffrin 1303 Feb 19 22:24 solving-knapsack-problem-a-recursive-solution.js
-rw-rw-r-- 1 jeffrin jeffrin 1366 Feb 21 23:17 greedy-algorithm-example-coin-change-problem.js
$
-l     use a long listing format
-r  reverse order while sorting
-t     sort by time, newest first
here you can see that the oldest date comes first  because  -r  is given for reverse sorting.
Here you can see the latest file for checking new things.

Create table on a database using python and MySQL

$python3  dt.py
$cat dt.py 
# importing required library
import mysql.connector

# connecting to the database
dataBase = mysql.connector.connect(
					host = "localhost",
					user = "jeff",
					passwd = "sixer",
					database = "learning" )

# preparing a cursor object
cursorObject = dataBase.cursor()

# creating table
studentRecord = """CREATE TABLE STUDENT (
				NAME VARCHAR(20) NOT NULL,
				BRANCH VARCHAR(50),
				ROLL INT NOT NULL,
				SECTION VARCHAR(5),
				AGE INT
				)"""

# table created
cursorObject.execute(studentRecord)

# disconnecting from server
dataBase.close()
$mysql --user=jeff -psixer
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 9
Server version: 8.0.30-1 (Debian)

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use learning;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> show tables;
+--------------------+
| Tables_in_learning |
+--------------------+
| STUDENT            |
+--------------------+
1 row in set (0.00 sec)

mysql> desc STUDENT;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| NAME    | varchar(20) | NO   |     | NULL    |       |
| BRANCH  | varchar(50) | YES  |     | NULL    |       |
| ROLL    | int         | NO   |     | NULL    |       |
| SECTION | varchar(5)  | YES  |     | NULL    |       |
| AGE     | int         | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
5 rows in set (0.20 sec)

mysql>

Connect MySQL database using MySQL-Connector Python

$cat fdb.py
import mysql.connector


conn = mysql.connector.connect(host='localhost',
			database='learning',
			user='jeff',
			password='sixer')
print(conn)
conn.close
$python3  fdb.py
<mysql.connector.connection_cext.CMySQLConnection object at 0x7f143fc84790>
$

Verifying MySQL Connector/Python installation

$python3
Python 3.10.6 (main, Aug 10 2022, 11:19:32) [GCC 12.1.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import mysql.connector
>>> 
>>> 
>>> mysql.connector.connect(host='localhost',
...                         database='learning',
...                         user='jeff',
...                         password='sixer')
<mysql.connector.connection_cext.CMySQLConnection object at 0x7f9ddd630400>
>>> 
$cat ted.py 
import mysql.connector


mysql.connector.connect(host='localhost',
			database='learning',
			user='jeff',
			password='sixer')
$

How to change root password of mysql on debian ?

$sudo mysql
[sudo] password for jeffrin: 
Sorry, try again.
[sudo] password for jeffrin: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.30-1 (Debian)

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'unix';
Query OK, 0 rows affected (0.46 sec)

mysql>

How to create a new user and grant permissions in MySQL and also creating a database ?

sudo mysql
[sudo] password for jeffrin: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 9
Server version: 8.0.30-1 (Debian)

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> CREATE USER 'jeff'@'localhost' IDENTIFIED WITH authentication_plugin BY 'sixer';
ERROR 1524 (HY000): Plugin 'authentication_plugin' is not loaded
mysql> CREATE USER 'jeff'@'localhost' IDENTIFIED BY 'sixer';
Query OK, 0 rows affected (0.49 sec)

mysql> CREATE DATABASE learning;
Query OK, 1 row affected (0.27 sec)

mysql> UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '('MyNewPass') WHERE User='root'' at line 1
mysql> UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '('MyNewPass') WHERE User='root'' at line 1
mysql> GRANT ALL PRIVILEGES ON *.* TO 'jeff'@'localhost' WITH GRANT OPTION;
Query OK, 0 rows affected (0.69 sec)

mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.14 sec)

mysql> 

How to install MySQL-Connector-Python module in Debian ?

$pip install mysql-connector-python
Defaulting to user installation because normal site-packages is not writeable

Collecting mysql-connector-python
  Downloading mysql_connector_python-8.0.30-cp310-cp310-manylinux1_x86_64.whl (25.4 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 25.4/25.4 MB 2.3 MB/s eta 0:00:00
Collecting protobuf<=3.20.1,>=3.11.0
  Downloading protobuf-3.20.1-cp310-cp310-manylinux_2_12_x86_64.manylinux2010_x86_64.whl (1.1 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 1.1/1.1 MB 1.4 MB/s eta 0:00:00
Installing collected packages: protobuf, mysql-connector-python
Successfully installed mysql-connector-python-8.0.30 protobuf-3.20.1

How to install mysql-connector method for python in Debian ?

$pip3 install  mysql-connector
Defaulting to user installation because normal site-packages is not writeable
Collecting mysql-connector
  Downloading mysql-connector-2.2.9.tar.gz (11.9 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 11.9/11.9 MB 2.0 MB/s eta 0:00:00
  Preparing metadata (setup.py) ... done
Building wheels for collected packages: mysql-connector
  Building wheel for mysql-connector (setup.py) ... done
  Created wheel for mysql-connector: filename=mysql_connector-2.2.9-cp310-cp310-linux_x86_64.whl size=247966 sha256=24d2cc6f0033919bd3bbe1a59ef54a72bc3f302b9c4526115dea2c95e17d4fa7
  Stored in directory: /home/jeffrin/.cache/pip/wheels/76/48/9b/da67ff1a18fe8e9d428f9b1a177716d4a7d363d2bbe83bf6cf
Successfully built mysql-connector
Installing collected packages: mysql-connector
Successfully installed mysql-connector-2.2.9
$ 

Program to POST a form using HTTP with requests

 
$cat  form_post_method.py 
#!/usr/bin/env python3

import requests

data_dictionary = {'custname': 'customer','custtel': '323232',
'size': 'large','custemail': 'email@domain.com'}
response = requests.post("http://httpbin.org/post",data=data_dictionary)

# we then print out the http status_code
print("HTTP Status Code: " + str(response.status_code))

if response.status_code == 200:
	print(response.text)
$python3  form_post_method.py 
HTTP Status Code: 200
{
  "args": {}, 
  "data": "", 
  "files": {}, 
  "form": {
    "custemail": "email@domain.com", 
    "custname": "customer", 
    "custtel": "323232", 
    "size": "large"
  }, 
  "headers": {
    "Accept": "*/*", 
    "Accept-Encoding": "gzip, deflate", 
    "Content-Length": "72", 
    "Content-Type": "application/x-www-form-urlencoded", 
    "Host": "httpbin.org", 
    "User-Agent": "python-requests/2.27.1", 
    "X-Amzn-Trace-Id": "Root=1-62fd14b6-46c6b0b363ae1c7571b8c3f0"
  }, 
  "json": null, 
  "origin": "27.57.31.195", 
  "url": "http://httpbin.org/post"
}

$       

Program to do digest authentication using requests module

$cat  digest_authentication.py 
#!/usr/bin/env python3

import requests
from requests.auth import HTTPDigestAuth

url = 'http://httpbin.org/digest-auth/auth/user/pass'
response = requests.get(url, auth=HTTPDigestAuth('user', 'pass'))
print('Response.status_code:'+ str(response.status_code))
if response.status_code == 200:
	print('Login successful :'+str(response.json()))
$
$python3 digest_authentication.py 
Response.status_code:200
Login successful :{'authenticated': True, 'user': 'user'}