Shell

Quick notes

System information

• neofetch, system info
• du -sh <file>/<directory>, check the size of file or directory
• df -h, display free disk space
  • -h, 1k = 1024 byte
  • -H, 1k = 1000 byte
• uname -s, print kernel name
  • Linux
  • Darwin
• uname -r, linux release number
• last -n 50, check last logged in users
• lastb -n 50,
• pstree -p, process tree
• w, show who is logged on and what they are doing

Auto delete files in tmp (CentOS 7)

• tmpwatch - removes files which haven’t been accessed for a period of time
  • install: yum install -y tmpwatch
  • delete files not accessed in 7 days: tmpwatch 7d /tmp
• cron 定期执行指定程序
  • crond
  • crontab -e
    • 0 0 * * * tmpwatch 7d /tmp

sed

Sed is the ultimate stream editor.

• Sed: http://www.grymoire.com/Unix/Sed.html
• Regular Expression: http://www.grymoire.com/Unix/Regular.html

Some examples:

• sed s/spaceship/honukai/g <old.file >new.file
• change = ““
  • sed -i.bak '/ZSH_THEME/s/".*"/"honukai"/'
    • backup old file to .bak
    • ZSH_THEME="robbyrussell" => ZSH_THEME="honukai"
• change =
  • sed -i.bak 's/^key\s*=.*/key = value/'
  • ^, start with
  • \s, space, tag, …

timezone

apt-get install tzdata
ln -fs /usr/share/zoneinfo/Asia/Shanghai /etc/localtime

file exist

file=data
if [ -f ${file} ]
then
    echo "$file found"
else
    echo "$file not found"
fi

• -d exists and is a directory
• -e exists
• -f exists and is a regular file
• -h exists and is a symbolic link

Symbol link

ln -sf <target> <symlink>

Example for glibc:

ln -sf libstdc++.so.6.0.21 libstdc++.so.6
strings /usr/lib64/libstdc++.so.6 | grep GLIBCXX

Open port in CentOS 7

firewall-cmd --permanent --add-port=8888/tcp
firewall-cmd --reload
firewall-cmd --list-ports

Create and delete user

Create user:

useradd <username> -b <base_dir> -e <expire_date>
echo <passwd> | passwd --stdin <username>

• -b, --base-dir, HOME_DIR=${BASE_DIR}/${USERNAME}
• -d, --home-dir
• -e, example: 2018-01-30

Delete user:

userdel -r <username>

• -f, force remove, even if the user is still logged in. Dangerous!
• -r, remove user’s home directory

The art of command line

https://github.com/jlevy/the-art-of-command-line

AMAZING!

• set -o vi, vi style command line
• !!, last command
• jq, JSON processor

man bash

• bash -c <string>, Docker use

TODO

List all versions

Yum.

yum --showduplicates list <package>
yum install <package>-<version>

Brew.

brew info <package>
brew search <package>@
brew install <package>@<version>
brew link <package>@<version> --force --overwrite