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Single branch (single branch is rarely used)

"check_mem.sh" 12L 318C 12J 1 all #! / bin/bashmt=$ (free | awk'/ ^ Mem:/ {print $2}') mu=$ (free | awk'/ ^ Mem:/ {print $3}') mu100=$ (expr $mu\ * 100 / $mt) [$mu100 -gt 1] & & echo "memory usage space has been exceeded Reached $mu100% "disk=$ (df | awk-F' [%] +'/\ / $/ {print $5}') if [$disk-gt 1] then echo" disk usage has exceeded, reached $disk% "fi

Less code without a single branch

#! / bin/bashmt=$ (free | awk'/ ^ Mem:/ {print $2}') mu=$ (free | awk'/ ^ Mem:/ {print $3}') mu100=$ (expr $mu\ * 100 / $mt) [$mu100-gt 1] & & echo "memory usage has exceeded, reaching $mu100%" disk=$ (df | awk-F' [%] +'/\ / $/ {print $5}') [$disk-gt 1] & & echo "disk usage has exceeded, reached $disk%"

Double branch

[root@bogon ~] # vim sfz.shangxinxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Else echo "Please keep trying!" Fi [root@bogon ~] # sh sfz.sh Please enter your score (range 1-100): 65 Please keep trying! [root@bogon ~] # sh sfz.sh Please enter your score (range 1-100): 90 your grades are excellent, keep it!

#! / bin/bash#-c 3 three ping packages #-I 0.2 interval 0.2s# $1 location variable #-W 1 corresponding timeout ping-c 3-I 0.2-w 1 $1 & > / dev/nullif [$?-eq 0] then echo "Host $1 is up." else echo "Host $1 is down." fi [root@bogon ~] # sh check_host.sh 192.168.200.111Host 192.168. 200.111 is up. [root@bogon] # sh check_host.sh 192.168.200.112Host 192.168.200.112 is down. [root@bogon] # sh check_host.sh 192.168.200.113Host 192.168.200.113 is down.

Multi-branch if statement structure: there is no limit to the number of elif. When the number is large, it is recommended to use case.

Read-p "Please enter a number:" numif [$(expr $num% 2)-eq 0] then echo "even number" else echo "odd number" [root @ bogon] # vim grade.shemaker Bash read-p "Please enter your test score (0-100):" numif [$num-ge 0] & [$num-le 100] then if [$num-le 100] & & [$num-ge 80] Then echo "excellent" elif [$num-le 79] & & [$num-ge 60] then echo "qualified" else echo "unqualified" fielse echo entered incorrectly "exit 2fi# exit 2 defines the return value as 2 [root@bogon ~] # sh grade .sh Please enter your test score (0100): 120incorrectly [root@bogon] # sh grade.sh Please enter your test score (0100): 100excellent [root@bogon] # sh grade.sh Please enter your test score (0100): 78 pass [root@bogon ~] # sh grade.sh please enter your test score (0100): 30 failed

two。 Patrol inspection alarm

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