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mongodb aggregates using MongoRepository in Java spring boot

---

Some prerequisites and assumptions

Use the following dependencies within your pom.xml:

• spring-boot-starter-parent 1.5.7.RELEASE
• spring-boot-starter-data-mongodb

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password creation

cli password generation

apg -a 1 -m 15 -n 15

Output

HrTvb(r&xb1~}Xr
`i;af,/z%bi8(`x

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hidden files

create an archive using tar (including hidden files)

taken from Digitesters

Normally:

tar czf backup.tar.gz /backup/*

This way all files are tarred except the hidden files.

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binary math

source

2's complement

101 -> 010 + 1 = 011
11010 -> 00101 + 1 = 00110

binary subtraction

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shifting bits

n << 1 == n * 2
n << 2 == n * 4
n << 3 == n * 8

n >> 1 == n / 2

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>>> a = 'world'    
>>> b = b'hello '    
>>> type(a)
<class 'str'>
>>> type(b)
<class 'bytes'>    

What's new in python3 shows:

>>> str.encode(a)

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docker cli

  -it

docker-compose

  stdin_open: true
  tty: true

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  $ namei -om ~/tmp/newnew/
  f: /home/user/tmp/newnew/
  drwxr-xr-x root   root   /
  drwxr-xr-x root   root   home
  drwxr-xr-x user user user
  drwxrwxr-x user user tmp
  drwxrwxr-x user user newnew

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ssh-agent bash -c ' ssh-add ~/git_key/id_rsa; cd ~/some_git_repo; git pull'

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source

Redirect stdout to one file and stderr to another file:

command > out 2>error

Redirect stderr to stdout (&1), and then redirect stdout to a file:

command >out 2>&1