一、while的特殊用法一： 一直循环，永不退出
while :;do
...
done
#!/bin/bash
# showfile.sh
while : ; do
read -p "Files path:" FILEPATH
[ $FILEPATH == ‘quit‘ ] && break
if [ -e $FILEPATH ];then
echo "$FILEPATH exists."
else
echo "No $FILEPATH."
fi
done
echo "Quit..."
[[email protected] yum.repos.d]# ./showfile.sh
Files path:/etc
/etc exists.
Files path:/etcc/
No /etcc/.
Files path:/yum/VT
/yum/VT exists.
Files path:quit
Quit...
二、while的特殊用法二： 将文本逐行处理
while read LINE; do
...
done < /PATH/TO/SOMEFILE
#!/bin/bash
# showfile.sh
FILE=/etc/passwd
let I=1
while read LINE;do
[ `echo $LINE |awk -F : ‘{print $NF}‘` == ‘/bin/bash‘ ] && echo $LINE |awk -F : ‘{print $1}‘ && let I++
[ $I -gt 2 ] && break
done <$FILE
[[email protected] yum.repos.d]# ./showuser.sh
root
./showuser.sh: line 6: [: ==: unary operator expected
oracle
区别continue与break运行机制：
#!/bin/bash
# odd.sh
let SUM=0
let I=0
read -p "keyin I:" I2
read -p "keyin SUM:" SUM2
while [ $I -lt $I2 ];do
let I++
if [ $[$I%2] -eq 1 ]; then
continue # 结束本轮或本次循环
fi
if [ $SUM -ge $SUM2 ] ;then
break # 提前退出此while循环体
fi
let SUM+=$I
done
echo "SUM=$SUM; I=$I"
[[email protected] yum.repos.d]# ./odd.sh
keyin I:100
keyin SUM:2000
SUM=2070; I=92
[[email protected] yum.repos.d]# ./odd.sh
keyin I:100
keyin SUM:200
SUM=210; I=30
[[email protected] yum.repos.d]# ./odd.sh
keyin I:1000
keyin SUM:20000
SUM=20022; I=284
三、自动查看bash脚本是否有问题，且显示错误后进入该脚本修改
#!/bin/bash
# syntax.sh
until bash -n $1 &> /dev/null; do
read -p "Syntax error,[Q|q] to quit,others for editing: " CHOICE
case $CHOICE in
q|Q)
echo "Something wrong,quiting..."
exit 5;;
*)
bash -n $1
sleep 5
vim + $1;;
esac
done
[[email protected] yum.repos.d]# ./syntax.sh hello.sh
Syntax error,[Q|q] to quit,others for editing:
hello.sh: line 2: syntax error near unexpected token `;‘
hello.sh: line 2: `while ;do‘
Syntax error,[Q|q] to quit,others for editing:
hello.sh: line 2: syntax error near unexpected token `;‘
hello.sh: line 2: `while ;do‘