Shell script programming string testing and looping

== : Two strings are equal

! =: Two characters not equal

> : Whether a string is greater than another string

< : Whether a string is less than another string

- N String : Tests whether the specified string is empty

- s string : Tests whether the specified string is not empty

For example

Determine if the user name is the same as the group name

#!/bin/bash

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

echo "Nouser"

Exit

Fi

If [' id–n–u ' = = ' id–n–u $ ']; Then

echo "OK"

Else

echo "Notok"

Fi

Write a script

pass a parameter to the script, if the argument is Q or Q or quit exit the script, or the user's parameters will be displayed

#!/bin/bash

# determine if a script exists

if [$ = ' Q ']; Then

echo "Exit"

Exit

elif [$ = ' Q ']; Then

echo "Exit"

Exit

elif [$ = ' quit ']; Then

echo "Exit"

Exit

elif [$ = ' Quit ']; Then

echo "Exit"

Exit

Elsee

echo $

Fi

Practice

Pass 3 parameters to the script, the first is an integer, the second is an arithmetic operator, and the third is the result of the calculation is displayed to preserve 2 for precision, shaped like ./CALC.SH5/2

tip: Calculate using BC command, in BC used in Scale the precision can be preserved, using echo "scale=2 ; 111/22 ; "| BC, keep it in a variable, directly referencing

Practice

write a script that determines the current main sentence CPU producers, whose information is /proc/cpuinfo in the file Evderid in a row

if the manufacturer AUTHENTICAMD is displayed as AMD Company, if the manufacturer is Genuineintel is displayed as Intel Company, otherwise it will show up as a non-mainstream company

Practice

write a script that passes to the script. 3 integers, interpreting the maximum and minimum numbers, and displaying the

you can set a variable max=0 , and then let MAX with the $ to compare , if greater than MAX it will $ value is assigned to the MAX , then let MAX with the $ to make comparisons, one analogy

Practice

Pass 3 parameters to the script parameters are user names, the user's account confidence is extracted to place in /tmp/testusers.txt file, and requires a line number at the beginning of each line

Loop: Specify entry condition Exit condition

for Loops

for variables inch List ( The number in the variable goes through the number in the list and exits )

Do

Loop body

Done

seq : [ number of steps to start in ] end number, this is an order to pass `` referencing command results

The variable is the default string at the beginning.

declare–i sum=0 : Defined as integral type

- x : defined as environment variable

#!/bin/bash

Declare–i sum=0

For I in (1..100)

Do

letsum=$[$SUM + $I];

Done

echo "The sum is: $SUM"

Practice

Say hello to every user in the system, that is, traverse each user

Use wc–l/etc/passwd

Lines= ' wc–l/etc/passwd | Cut–d ' –f1 '

For I in ' seq 1 $LINES '

Do

echo "Hell ' head–n $I/etc/passwd | Tail-1 | Cut–d:-f1 ' "

Done

Write a script

Set Variable FIFE the value is /etc/passwd , once want to /etc/passwd say hello to each user and show the Shell , shaped like Helloyourshell : /bin/bash , Count the total number of users, and point to the default user greeting

Write a script

Add Ten a user User1 to the User10 , the password is the same as the user name, but only if the user name does not exist can be added, extended: accept a parameter Add : Add User User1...user10 , del : Delete User User1...user10 , the other exits

Write a script

Calculation - all that can be 3 The and of positive integers that are evenly divisible ( modulus, residual % 3%2=1)

Write a script

Calculation - within the sum of all the odd and all the even and, respectively displayed

write a script that shows all the defaults on the current system, respectively Shell to be Bash the user and default Shell to be /sbin/nologin users, and statistics of various Shell The total number of users below displays the resulting shape as

BASH , 3users , they is :

Root , Redhat , Gentoo

Nologin , 2users , they is :

bin , FTP

This article is from the Linux root file system blog, so be sure to keep this source http://amazonjian.blog.51cto.com/9604681/1709966

Shell script programming string testing and looping