while loop
? Syntax while condition; do…; done
? Case 1
#!/bin/bash
while :
do
load=w|head -1|awk -F'load average: ''{print $2}'|cut -d. -f1
if [$load -gt 10 ]
then
top|mail -s “load is high: $load” [email protected]
fi
sleep 30
done
: means an endless loop, also Can be written as 1 or true
Get load
[[email protected] ~]# uptime|awk -F’load average: ”{print $2}’|cut -d. -f 1
0–Include spaces when specifying delimiters
[[emailprotected] ~]# uptime|awk -F’load average:”{print $2}’|cut -d.- f 1
0 returns more spaces and more spaces
[[email protected] whiletest]# cat load.sh
#!/bin/bash
while :
do
load=w|head -1|awk -F'load average: ''{print $2}'|cut -d. -f1
if [$load -gt 10]
then
top|echo “load is high: $load”
fi
sleep 30
done
#!/bin/bash
while :< br>do
read -p “Please input a number: “n
if [-z “$n” ]
then
echo “you need input sth.”
continue
fi
n1=echo $n|sed's/[0-9]//g'
if [-n “$n1” ]then
echo “you just only input numbers.”
continue
fi
break
done
echo $n
continue–means continue above The loop
n1=echo $n|sed's/[0-9]//g' represents a purely numeric variable
break is also possible Used in a for loop
Out of the loop
#!/bin/bash
for i in seq 1 5
do
echo $i< br>if [$i == 3 ]
then
break
fi
echo $i
done
echo aaaaaaa
== compare strings, Numbers generally use eq
Why are they output twice? The first echo after –do prints a 1, and then judges that it is not equal to 3, and then prints again after fi
Usage of continue
End this cycle
# !/bin/bash
for i in seq 1 5
do
echo $i
if [$i == 3 ]
then
continue
fi
echo $i
done
echo $i
continue is to continue execution, and break is to start again
exit
< p>#!/bin/bash
for i in seq 1 5doecho $iif [$i == 3 ]thenexitfiecho $idoneecho aaaaaaa
< /p>