Shell condition judgment

Before we begin, take a look at the logical judgment symbols: & & and, | or! Non-A & & B must be established at the same time in order to pass the judgment-> judgment process: first execute A to determine whether it is established, and if it is established, continue to execute B to determine whether it is established-- > if it is not established, then directly end, no longer execute BA | | BA, B has an establishment, you can pass the judgment! An if An is not true, then by judging the number and symbol, as follows: comparison value: equal to-- >-- eq does not equal->-ne less than-- >-- lt greater than-- >-- gt less than or equal->-- le greater than or equal to->-ge some English words: help to remember some English words: equal equal to, not equal not equal, less than less than, great than greater than less equal less than or equal to great equal.

Comparison string: = equal, = equal, same =,! = not equal, > greater than, the application source code is as follows: [root@linux4 ~] # if [- d / root]; then / / to determine whether the root directory exists

> echo "ok" / / if there is an input OK

> fi

Ok## practical 2:if dual Branch Application-> pinghost.sh

Ping-c 3-I 0.2-w 3 192.168.1.1 the number of packets sent by Murc-I the interval between each packet sent. The default unit: second (s)-w waiting time. The source code that exceeds the return failure is as follows: #! / bin/bash# ping a given host and print the host status

Ip=192.168.1.1

Ping-c 3-I 0.2-w 3$ ip > > / dev/null #-c count-I?-w wait?

If [$?-eq 0]; then?

Echo "the host $ip is up."?

Else

Echo "the host $ip is down."?

Fi## actual combat 3:if multi-branch application-> judge numerical interval num.sh

The source code is as follows: #! / bin/bashread-p "Please enter a score:" numif [$num-gt 85-a $num-lt 100]; then

Echo 'excellent!'

Elif [$num-gt 70]; then

Echo 'good!'

Elif [$num-gt 60]; then

Echo 'qualified!'

Else

Echo 'not qualified!'

Fi

# # practical 4:if nesting use

The source code is as follows: #! / bin/bash

Read-p "Please enter the student's grade:" a

If [$a-lt 10]; then

Echo "Congratulations to this student on reaching the finals!"

Read-p "Please enter the classmate's gender:" b

If [$b = "male"]; then

Echo "Congratulations to this student on entering the men's final group!"

Else

Echo "Congratulations to this student on entering the women's final group!"

Fi

Fi