% Shell Usage 

# 用sudo重新执行上一条命令 | Re-call last input with sudo
sudo !!

# 帮助 | Help
help cd / help dir (...)

# 查找帮助 | Finding Help
apropos directory / apropos search (...)

# 定义自定义启动屏幕 | Define custom startup screen
sudo nano /etc/motd

# 以后台进程运行脚本 | Run a script as background process
<process> &

# 列出所有正在运行的进程 | List all running processes
ps -A

# 终止正在运行的进程 | Kill a running process
killall <Process-name>

% Shell System

# 获取当前路径 | Get the current path
pwd

# 获取当前主机名 | Get the current hostname
hostname

# 获取当前用户 | Get the current users
users

# 显示日历 | Show calendar
cal

# 显示当前日期 | Show today's date
date

# 退出终端 | Exit terminal
exit

% Shell Permissions

# 使用-R选项递归更改权限 | Use -R option to change permissions recursively.
ps -ef | grep apache | grep -v grep

# 更改组 | Change group
chgrp <group-name-from> <group-name-to>

% Shell Directories

# 列出目录内容 | List directory contents
ls

# 列出所有目录内容 | List all directory contents
ll

# 按编辑时间列出所有目录内容 | List all directory contents sorted by time edited
ls -alt

# 列出目录（通配符匹配） | List directory (wildcard matching)
ls *.<txt>

# 列出指定类型的所有文件 | List all files of type
find . -name '*.<txt>' -print

# 返回上一个目录 | Go back to previous directory
cd -

# 创建（空）目录 | Make (empty) directory
mkdir <dirname>

# 删除（空）目录 | Remove (empty) directory
rmdir <dirname>

# 无提示删除目录及其所有内容 | Remove directory with all contents without prompt
rm -rf <dirname>

# 删除目录内容但保留目录 | Remove directory contents and keep directory
rm -rf *

# 切换目录 | Change directory
cd <dirname>

% shell Symlinks

# 创建符号链接 | Create symlink
ln -s <source-dirname> <destination-dirname>

# 更新符号链接 | Update symlink
ln -sfn <source-dirname> <destination-dirname>

# 删除符号链接 | Remove symlink
unlink <sample-dirname>

% Shell Files

# 创建（空）文件 | Make (empty) file
touch <filename-txt>

# 复制文件 | Duplicate file
cp <filename> <file-copyname>

# 复制/分页文件夹及其内容 | Copy/Page folder with content
cp -a <old-folder>/ <new-folder>

# 移动/重命名文件 | Move/Rename file
mv <current-filename-path> <new-filename-path>

# 移动/重命名文件并在覆盖现有文件前提示 | Move/Rename file and prompt before overwriting an existing file
mv -i <current-filename> <new-filename>

# 删除文件 | Remove file
rm <filename-txt>

# 写入文件（将覆盖现有内容） | Write to file (will overwrite existing content)
cat > <filename-txt> 

# 在当前目录中搜索文件名（非内容） | Search for a filename-(not content!) in the current directory
find <filename-txt>

# 在当前目录和子目录的所有文件中搜索字符串 | Search for a string inside all files in the current directory and subdrectories
grep -r <string> *

# 在文件中搜索并替换 | Search and replace within file
sed -i s/<original-text>/<new-text>/g <filename-txt>

# 文件的MD5哈希值 | MD5 hash for files
md5 <filename-txt>

# 文件夹的MD5哈希值 | MD5 hash for folders
tar c <folder> | md5sum

# 加密文件 | Encrypt file
openssl enc -aes-256-cbc -e -in <sample-filename-txt> -out <sample-encrypted-txt>

# 解密文件 | Decrypt file
openssl enc -aes-256-cbc -d -in <sample-encrypted> -out <sample-filename>

% Shell Server

# 通过ssh访问 | Access via ssh
ssh <username_remote>

# 从服务器复制文件到本地 | Copy file from server to local
scp <username_remote>:<file-to-send-path> <path-to-recieve> 

# 从本地复制文件到服务器 | Copy file from local to server
scp <file-to-send> <username_remote>:<where-to-put>

# 转义文件名中的空格 | Escape files with spaces in name like this
<path-to-file>\\\ <name-png>

$ username_remote: cat ~/.ssh/config | grep -i "host "|sed 's/^[ \t]*//g' | awk '{print $2}'

% Shell System

# 显示磁盘空间 | Show disc space
df -h

# 显示磁盘空间（inode） | Show disc space (inodes)
df -i

# 显示当前目录的磁盘空间 | Show disc space for current directory
du -hs

# 当前进程（包括CPU使用率） | Current processes (also CPS usage)
top or htop

# 显示正在运行的php进程 | Show running php processes
ps aux | grep php

# 监控错误日志（实时显示文件增长） | Monitor error log (stream as file grows)
tail error.log -f -n 0

% Shell Apps

# 启动应用程序 | Start appliction
xdg-open <programme> 

# 用当前文件夹打开Finder | Open finder with current folder
open .

% Shell Variables

# 注册变量 | Register variable
export <TESTING>=<Variable-text>

# 输出变量 | Echo variable
echo $<Variable>

# 取消设置变量 | Unset variable
unset <Variable>

% Shell Output & Redirects

# 写入文件 | Write to file
echo <Hello> > <hello-txt>

# 将一个文件的内容追加到另一个文件 | Append content from a file to another file
cat <file1-txt> >> <file2-txt>

# 将行数、单词数和字符数添加到<file2-txt> | Add the amount of lines, words, and characters to <file2-txt>
cat <file1-txt> | <word-count> | cat > <file2-txt>

# 对文件内容进行排序（类似cat） | Sort the content of a file (like cat)
sort <hello-txt>

# 将排序后的内容保存到新文件 | Save to sorted content to a new file
cat <file1-txt> | sort > <sorted-file1-txt>

# 排序并去重后保存到新文件 | Sort and remove duplicates and save to a new file
sort <file1-txt> | uniq > <uniq-file1-txt>