cat file.txt //show the content of file.txt 显示file.txt中的内容
cat file.txt file1.txt.... //show the content of file.txt file1.txt ..... 显示多个文件file.txt file1.txt...的内容
cat file.txt | tr -s '\n' //show the content of file.txt. It will squeeze adjacent '\n' characters into a single '\n' 显示file.txt的内容，并且将连续的空行换成一个
cat -T file.txt //show the content of file.txt and highlight tab characters as ^I 显示file.txt中的内容，并且将TAB自付显示为^I
cat -n file.txt //show each line with a line number prefixed 显示文件中的内容，每一行带有行号
cat file1.txt file3.txt | xargs //show the content of file1.txt and file3.txt without any enter '\n'
cat file1.txt | xargs -n 3 //Converting single line into multiple line output and every line has 3 words (the default delimiter is space, so we could thinks it as words)

find base_path //list all files and subfiles in base_path
find /root/deploy_ws/ -name "testlist.*" //list all files with filename starting with testlist in /root/deploy_ws
find /root/deploy_ws/ -iname "testlist.*" //list all files with filename starting with testlist in /root/deploy_ws, the more important is to ignore case
find /root/deploy_ws \( -name "testlist.*" -or -name "*.plugin" \) -print //list all files with filename starting with testlist or ending with plugin
find /root/deploy_ws \( -name "testlist.*" -and -name "*.plugin" \) //list all files with filename starting with testlist and ending with plugin
find /root/deploy_ws -path "*BAT*" -print //list all files in /root/deploy_ws and the path for the files should match BAT*
find . -regex ".*\(\.txt\|\.sh\)$" //list all files with filename ending with txt or sh in current dir.
find . ! -name "*.txt" -print    //list files the name does not end with .txtfind . -type d -print  //List only directories including descendantsfind . -type f -print  //List only regular filesfind . -type l -print //List only symbolic linksfind /usr/lib/firefox/plugins -type l -print  //list symbolic links in /usr/lib/firefox/pluginsfind . -type f -name "*.sh" -delete  //delete all files whose type is file and filename end with .sh

#echo "HELLO WHO IS THIS" | tr 'A-Z' 'a-z'
hello who is this

#cat file1.txt
This is the first line inside file1.txt
# cat file1.txt | tr -d 'first'
Th  he  lne nde le1.x

# echo hello 1 char 2 next 4 | tr -d -c '0-9 \n'   1  2  4

# echo aaacccddd | tr -s [a-z]
acd

#mkdir -p /root/deploy_ws/shellTest/newDir/newDir    //ignores if any level of directory exists and creates the missing directories.