Bash's three script exercises and arithmetic operations

Exercise: Write a script

Determine if there is a user's default shell for bash on the current system;

If so, the number of such users is displayed, otherwise no such user is shown

#!/bin/bash

Acount= ' grep ' \<bash$ '/etc/passwd |wc-l '

If [$acount-gt 0];then

echo "There has $acount such users"

Else

echo "No such users"

Fi

Exercise: Write a script

Given a file, such as/etc/inittab

Determine if there is a blank line in this file

If so, displays the number of blank lines; otherwise, no blank lines are displayed;

#!/bin/bash

I= ' grep ' ^$ '/etc/inittab|wc-l '

If [$i-gt 0];then

echo "There is $i blank lines"

Else

echo "No Blank Lines"

Fi

Exercise: Write a script

Given a user, determine if the UID is the same as the GID

If it does, the user is displayed as "good guy";

[' Id-u user1 '-eq ' id-g user1 ']&& echo ' good guy ' | | echo "Bad guy"

Exercise: Write a script

Given a user, get the password warning period;

And then determine whether the user last modified password time is less than the maximum age of the warning period;

If less than. "Warning" is displayed; otherwise, "OK" is displayed;

Tip: The method of arithmetic operation $[$A-$B], which represents the value of variable A minus the value of variable B

#!/bin/bash

if! ID $ &>/dev/null;then

echo "User $ no exists!"

Else

Wtime= ' grep ' $ '/etc/shadow|cut-d:-f6 '

Ctime= ' grep ' $ '/etc/shadow|cut-d:-f3 '

Utime= ' grep ' $ '/etc/shadow|cut-d:-f5 '

now= ' Date +%s/86400|bc '

ltime=$[$utime-$[$now-$ctime]

If [$ltime-lt $wtime];then

echo "warning!"

Else

echo "OK"

Fi

Fi

Exercise: Write a script

What is the total entry for the history command in the decision command history?

[Email protected] ~]# history |tail-1|cut-d '-f3

568

Note: It is not possible to use the history |wc-l to calculate, because the historical command can store the size of the environment variable histsize, and overflow when it exceeds, our topic means to count the historical commands that have been used.

How to perform arithmetic operations in the shell:

A=3

B=7

1. Let arithmetic expression

Let c= $A + $B

2. $[arithmetic operation expression]

$[$A + $B]

3, $ (arithmetic operation expression)

$ (($A + $B))

4. Expr arithmetic expression, the action in the expression and the operator must have a space between, and the assignment requires a command reference

c= ' expr $A + $B '

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Bash's three script exercises and arithmetic operations