sometimes you will write shell in windows platform, be careful for this, adjust the notepad plus plus information.

/etc/profile
A global configuration script that applies to all users.

~/.bash_profile
A user's personal startup file. Can be used to extend or override settings in the global configuration script.

~/.bashrc
A user's personal startup file. Can be used to extend or override settings in the global configuration script.

command << token
content to be used as command's standard input token

command >>file.txt command >file.txt ,pipe redirect the content to file.

>> append to the file >overwrite the file

Assigning A Command's Result To A Variable

You can also assign the results of a command to a variable:

right_now=$(date +"%x %r %Z")

Constants

IFS=$’\n’

Exit Status

Commands (including the scripts and shell functions we write) issue a value to the system when they terminate, called an exit status. This value, which is an integer in the range of 0 to 255, indicates the success or failure of the command’s execution. By convention, a value of zero indicates success and any other value indicates failure.

Expression

d file

True if file is a directory.

-e file

True if file exists.

-f file

True if file exists and is a regular file.

exit

In order to be good script writers, we must set the exit status when our scripts finish.

exit 0

exit 1

Positional parameters are a series of special variables ($0 through $9) that contain the contents of the command line.