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Peiwen Li
Peiwen Li

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Daily Notes: Useful Commands

#devops #linux #beginners

Originally written on 2020-03-10. DEV's displayed publication date reflects this archive migration.

Commands are difficult to remember, and easy to forget, so here's a common command repository

  • UPDATE pip packages

    $ pip install --upgrade django-mailer==2.0.1
# pip <command> <option> <package-name>==<version.number>

  • COPY file from one dir to another

    $ cp -i path/to/file.py path/to/dir/
# -i is for interactive, will be asked to replace any files

  • CREATE a directory with this date:

    # create a directory with this date:
$ mkdir "$(date '+%Y-%m-%d')"
# dir name: 2020-03-10
$ mkdir "$(date '+%Y-%m-%d--%H-%M-%S')"
# dir name: 2020-03-10--11-03-01

$ mkdir "$(TZ=UTC-8  date '+%Y-%m-%d--%H-%M-%S')"
# dir name: 2020-03-10--13-10-59 (Beijing time)
$ mkdir "$(TZ=UTC-0  date '+%Y-%m-%d--%H-%M-%S')"
# dir name: 2020-03-10--05-11-05 (Greenwich time)

  • RSYNC a remote file to local through pipe

    # rsync a remote file to local
$ rsync -avz -e ssh user@ip_add:~/remote_dir/file local_dir/
# '-e' is essential for creating an ssh connection

  • check mac environment variable

    $ printenv

    check a specific variable

    $ echo $variable_name

    If setting more permanent environment variables:

    For system-wide operations, it should be in /etc/profile

    For user based operations, it should be in ~/.bash_profile

    For non-login interactive shells, it should be in ~/.bashrc

    For better understanding, you better check out this: Unix Introduction — Shell

  • Look for files: whereis

    $ whereis python3
/usr/bin/python3

  • locale

    # check your locale setting
$ locale
# update it
$ sudo update-locale LANG="en_US.UTF-8" LANGUAGE="en_US.UTF-8"

  • make nested dir

    $ mkdir -p _backups/_archives

vim basic 

输入：
i (insert, start editing)
: w filename （将文章以指定的文件名filename保存）
: wq (输入「wq」，存盘并退出vim)
: q! (输入q!， 不存盘强制退出vim)
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The Many Uses of Rsync

It’s faster than scp (Secure Copy) because rsync uses remote-update protocol which allows to transfer just the differences between two sets of files. First time, it copies the whole content of a file or a directory from source to destination but from next time, it copies only the changed blocks and bytes to the destination.

# basic format
# $ rsync <options> <source> <destination>

$ rsync -av path/to/directory1/ /path/to/directory2/ 
$ rsync -av path/to/directory1 /path/to/directory2/ 
# there's a difference: copy the files in that folder or the folder itself
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The flags/options:

  • -a: archive mode, archive mode allows copying files recursively and it also preserves symbolic links, file permissions, user & group ownerships and timestamps
  • -v: As with many other commands, this option asks for verbose output. This is especially useful when copying large amounts of data.
  • -r : copies data recursively (but don’t preserve timestamps and permission while transferring data
  • -z : compress file data
  • -h : human-readable, output numbers in a human-readable format
  • –delete: This flag isn’t used here but it is a common feature of rsync. This option deletes any files or folders in the destination that aren’t at the source. Use with extreme caution!
  • -h or –help: This prints a help page that has useful information about using rsync.

zip, copy remotely, remove source files 

# use tar command to archive the files, django-archive is used to backup databases in my project
$ tar -zcvf backup1.tar.gz path/to/files/
# or create with a timestamp
$ tar -zcvf "$(date '+%y-%m-%d').tar.gz" path/to/files/

$ rsync -avz --remove-source-files path/to/backup1 user@ip_add:/path/to/backups/
# with a timestamp
$ rsync -avz --remove-source-files "$(date '+%y-%m-%d').tar.gz" user@ip_add:/path/to/backups/
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