1，判断
if .. then ..fi
if .. then ,,else.. fi
if ..then.. elif ..then.. else ... fi 语句
======================================
#!/bin/sh
a=10
b=20
if [ $a == $b ]
then
echo "a is equal to b"
fi
if [ $a != $b ]
then
echo "a is not equal to b"
fi
============================================
#!/bin/sh
a=10
b=20
if [ $a == $b ]
then
echo "a is equal to b"
else
echo "a is not equal to b"
fi===================================================#!/bin/sh
a=10
b=20
if [ $a == $b ]
then
echo "a is equal to b"
elif [ $a -gt $b ]
then
echo "a is greater than b"
elif [ $a -lt $b ]
then
echo "a is less than b"
else
echo "None of the condition met"
fi====================================================
2,循环
for loop in 1 2 3 4 5
do
echo "The value is: $loop"
done================================================COUNTER=0
while [ $COUNTER -lt 5 ]
do
COUNTER='expr $COUNTER+1'
echo $COUNTER
done======================================================#!/bin/bash
a=0
until [ ! $a -lt 10 ]
do
echo $a
a=`expr $a + 1`
done=======================================================3多分支
case 值 in
模式1)
command1
command2
command3
;;
模式2）
command1
command2
command3
;;
*)
command1
command2
command3
;;
esac
===========================================#!/bin/bash
option="${1}"
case ${option} in
-f) FILE="${2}"
echo "File name is $FILE"
;;
-d) DIR="${2}"
echo "Dir name is $DIR"
;;
*)
echo "`basename ${0}`:usage: [-f file] | [-d directory]"
exit 1 # Command to come out of the program with status 1
;;
esac