A detailed description of the arithmetic operators for Bash programming under Linux (iii)

A detailed description of the arithmetic operators for Bash programming under Linux (iii)

The shell arithmetic operation is represented as follows:

1. Let arithmetic operation expression

Let c= $A + $B

2. $[arithmetic operation expression]

c=$[$A + $B]

3, $ (arithmetic operation expression)

c=$ (($A + $B))

4. Expr must have a space between each operand and operator, and you want to use a command reference

c= ' expr $A + $B '

To illustrate:

1. Specify a user to determine whether the remaining lifetime of the user's password is less than the warning period;

Show "Password will expire-Warning" if it is less than the warning period; otherwise, "OK" is displayed

Tip: The maximum usage period minus the number of days that have been used is the remaining period of use;

Vim shadowdate.sh Create a script file and add the following:

#!/bin/bash

Username=willow Specify a user and set the variable

Rece= ' grep ' \< $USERNAME \> "/etc/shadow | cut-d:-f3 ' recent password change time

long= ' grep ' \< $USERNAME \> "/etc/shadow | cut-d:-f5 ' Maximum password usage period

Expi= ' grep ' \< $USERNAME \> "/etc/shadow | cut-d:-f6 ' warning period

Curr= ' Date +%s ' from 1970/01/01 to today, total number of seconds

Let today= $CURR/86400 from 1970/01/01 to today, how many days

#let userdays= $TODAY-$RECE notes: How many days a password has been used one of the table method methods

#USERDAYS =$[$TODAY-$RECE] Notes: How many days the password has been used one of the two table method

userdays=$ (($TODAY-$RECE)) password has been used for how many days one of the three table method

left= ' expr $LONG-$USERDAYS ' remaining period of use

If [$LEFT-lt $EXPI]; Then

echo "Password'll expire-Warning"

Else

echo "Password is OK"

Fi

650) this.width=650; "src=" Http://s5.51cto.com/wyfs02/M01/7E/FD/wKiom1cPA2uDae_9AAJfGcvYkYg712.jpg "title=" Shadowdate.jpg "alt=" Wkiom1cpa2udae_9aajfgcvykyg712.jpg "/>

chmod a+x shadowdate.sh granted execution rights

./shadowdate.sh Execute Script

This article is from the "Xavier Willow" blog, please be sure to keep this source http://willow.blog.51cto.com/6574604/1763691

A detailed description of the arithmetic operators for Bash programming under Linux (iii)