Linux special Variables

$ # Parameter serial number sent to the shell command

$-Options are provided when shell is started or the set command is used

$? Value returned after the previous command is executed

$ Process ID of the Current Shell

$! Process ID of the previous sub-process

$ @ All parameters, each enclosed in double brackets

$ * All parameters, enclosed in double brackets

$ N location parameter value; n indicates location

$0 Current Shell Name

$ * All command line parameters

$ @ Same as above

"$ *" Treats all command line parameters as one

"$ @" Gets the entire parameter list and separates it into different parameters.

 

[Example]

For VaR in $ * # Try $ *, $ @, "$ *", "$ @"

Do

Echo $ VaR

Done

The following script backs up all the target files to be edited to the/bak directory, and keeps all paths unchanged, such as VII/etc/hosts, copy/etc/hosts to/bak/etc/hosts.

# Cat/SH/VII

#! /Usr/bin/bash

# Check whether the target file exists before performing the backup operation

If [-F "$1"]; then

# Create a function to enable any key to continue

# If stty raw is not recognized on your machine, replace the raw in the two parts of the function with cbreak.

Get_char ()

{

Savedstty = 'stty-G'

Stty-echo

Stty raw

Dd If =/dev/tty BS = 1 COUNT = 1 2>/dev/null

Stty-raw

Stty echo

Stty $ savedstty

}

# Create the backup root path/bak and grant everyone the write permission

If [! -D "/bak"]; then

Mkdir/bak

Chmod A + w/bak

Fi

# Determine the path of the target file and create it so that everyone has the write permission on any newly created level directory.

Echo $1 | grep "/">/dev/null

If ["'echo $? '"=" 0 "]; then

CD $ {1% /*}

Fi

Pwdnow = 'pwd'

Path =/bak $ {pwdnow}

# Echo $ path

If [! -D "$ path"]; then

Mkdir-p $ path

Patha =$ {pwdnow #/}

Chmod-r a + w/bak/$ {patha % /*}

Fi

# Copying the target file

Datenow = 'date + % Y % m % d'

Timenow = 'date + % H % m % s'

/Usr/bin/CP $1 $ {path}/$ {1 # */}. $ {datenow}. $ {timenow}

Echo "target file \" $1 \ "has been copied to $ {path}/$ {1 # */}. $ {datenow}. $ {timenow }"

Echo "now going to \" VI $1 \ ", Press any key to continue ..."

Char = 'get _ char'

Fi

# Call the VI command

VI $1

Call scripts

# Chmod A + x/SH/VII

#/SH/VII/etc/passwd

You can add/sh to the path variable to make it easier.

Reprinted from http://xuxd32.blog.163.com/blog/static/48121933200922123138638/