shell脚本中的逻辑判断

1.if then fi

[[email protected] shell]# cat if1.sh
#!/bin/bash
a=5
if [ $a -gt 3 ]
then
       echo ok
fi

2.if then else fi：

[email protected] shell]# sh -x if2.sh
+ a=1
+ ‘[‘ 1 -gt 3 ‘]‘
+ echo nook
nook
[[email protected] shell]# cat if2.sh
#!/bin/bash
a=1
if [ $a -gt 3 ]
then
       echo ok
else
       echo nook
fi

3.if then elif then else fi：

[[email protected] shell]# cat if3.sh
#!/bin/bash
a=4
if [ $a -gt 4 ]
then
       echo ">1"
elif [ $a -lt 4 ]
then
       echo "<4"
else
       echo "=4"
fi

[[email protected] shell]# sh -x if3.sh
+ a=3
+ ‘[‘ 3 -gt 4 ‘]‘
+ ‘[‘ 3 -lt 4 ‘]‘
+ echo ‘<4‘
<4
[[email protected] shell]# vi if3.sh
[[email protected] shell]# sh -x if3.sh
+ a=4
+ ‘[‘ 4 -gt 4 ‘]‘
+ ‘[‘ 4 -lt 4 ‘]‘
+ echo =4
=4
[[email protected] shell]# cat if3.sh
#!/bin/bash
a=4

4.注意【】两侧都需要有空格，-gt 大于 -lt 小于 -eq等于 两侧都需要空格 -ge大于等于 -le小于等于 noeq 不等于

5.if逻辑判断支持||和&&

文件目录属性判断

1.-f file 判断是否是普通文件，且存在

[[email protected] shell]# sh -x file1.sh
+ f=/tmp/aminglinux
+ ‘[‘ -f /tmp/aminglinux ‘]‘
+ touch /tmp/aminglinux
[[email protected] shell]# cat file1.sh
#!/bin/bash
f="/tmp/aminglinux"
if [ -f $f ]
then
    echo $f exist
else
    touch $f
fi
[[email protected] shell]# sh -x file1.sh
+ f=/tmp/aminglinux
+ ‘[‘ -f /tmp/aminglinux ‘]‘
+ echo /tmp/aminglinux exist
/tmp/aminglinux exist

2.-d file 判断是否是目录且存在：

[[email protected] shell]# sh -x file2.sh
+ f=/tmp/aminglinux
+ ‘[‘ -d /tmp/aminglinux ‘]‘
+ touch /tmp/aminglinux
[[email protected] shell]# cat file2.sh
#!/bin/bash
f="/tmp/aminglinux"
if [ -d $f ]
then
    echo $d exist
else
    touch $f
fi

3.-e判断文件或者目录是否存在：

[[email protected] shell]# vi file2.sh
[[email protected] shell]# sh -x file2.sh
+ f=/tmp/aminglinux
+ ‘[‘ -e /tmp/aminglinux ‘]‘
+ echo exist
exist

4.-r判断文件是否可读

[[email protected] shell]# sh -x file2.sh
+ f=/tmp/aminglinux
+ ‘[‘ -r /tmp/aminglinux ‘]‘
+ echo /tmp/aminglinux readable
/tmp/aminglinux readable
[[email protected] shell]# cat file2.sh
#!/bin/bash
f="/tmp/aminglinux"
if [ -r $f ]
then
    echo $f readable
fi

5.-w判断文件是否可写

[[email protected] shell]# cat file2.sh
#!/bin/bash
f="/tmp/aminglinux"
if [ -w $f ]
then
    echo $f writeable
fi
[[email protected] shell]# sh -x file2.sh
+ f=/tmp/aminglinux
+ ‘[‘ -w /tmp/aminglinux ‘]‘
+ echo /tmp/aminglinux writeable
/tmp/aminglinux writeable

6.-x判断是否可执行：不可执行，没有输出

[[email protected] shell]# ls -l /tmp/aminglinux
-rw-r--r-- 1 root root 0 4月  18 21:36 /tmp/aminglinux
[[email protected] shell]# vi file2.sh
[[email protected] shell]# cat file2.sh
#!/bin/bash
f="/tmp/aminglinux"
if [ -x $f ]
then
    echo $f exeable
fi
[[email protected] shell]# sh -x file2.sh
+ f=/tmp/aminglinux
+ ‘[‘ -x /tmp/aminglinux ‘]‘

if特殊用法

1.判断变量是否为空：

++ wc -l /tmp/lalal
wc: /tmp/lalal: 没有那个文件或目录
+ n=
+ ‘[‘ -gt 100 ‘]‘
if4.sh: 第 3 行:[: -gt: 期待一元表达式
[[email protected] shell]# vi if4.sh
[[email protected] shell]# sh -x if4.sh
++ wc -l /tmp/lalal
wc: /tmp/lalal: 没有那个文件或目录
+ n=
+ ‘[‘ -z ‘‘ ‘]‘
+ echo error
error
[[email protected] shell]# cat if4.sh
#!/bin/bash
n=`wc -l /tmp/lalal`
if [ -z "$n" ]
then
   echo  error
elif [ $n -gt 100 ]
then
    echo aldkjglka
fi

2.-n判断是否不为空：

[[email protected] shell]# ls
01.sh  file1.sh  file2.sh  if1.sh  if2.sh  if3.sh  if4.sh
[[email protected] shell]# if [ -n 01.sh ]; then echo ok; fi
ok

3.-q 文件中含有字符时会怎样：

[[email protected] shell]# if grep -wq ‘weixing01‘ /etc/passwd; then echo "sdjfk"; fi
sdjfk

case判断

1.编写脚本：

[[email protected] shell]# cat case1.sh
 #!/bin/bash
read -p "Please input a number: " n
if [ -z "$n" ]
then
    echo "Please input a number."
    exit 1
fi

n1=`echo $n|sed ‘s/[0-9]//g‘`
if [ -n "$n1" ]
then
 echo "Please input a number."
 exit 1
fi

if [ $n -lt 60 ] && [ $n -ge 0 ]
then
    tag=1
elif [ $n -ge 60 ] && [ $n -lt 80 ]
then
    tag=2
elif [ $n -ge 80 ]  && [ $n -lt 90 ]
then
    tag=3
elif [ $n -ge 90 ] && [ $n -le 100 ]
then
    tag=4
else
    tag=0
fi
case $tag in
    1)
    echo "not ok"
        ;;
    2)
        echo "ok"
        ;;
    3)
        echo "ook"
        ;;
    4)
        echo "oook"
        ;;
    *)
        echo "The number range is 0-100."
        ;;
esac

[[email protected] shell]# sh -x  case1.sh
+ read -p ‘Please input a number: ‘ n
Please input a number: 101
+ ‘[‘ -z 101 ‘]‘
++ echo 101
++ sed ‘s/[0-9]//g‘
+ n1=
+ ‘[‘ -n ‘‘ ‘]‘
+ ‘[‘ 101 -lt 60 ‘]‘
+ ‘[‘ 101 -ge 60 ‘]‘
+ ‘[‘ 101 -lt 80 ‘]‘
+ ‘[‘ 101 -ge 80 ‘]‘
+ ‘[‘ 101 -lt 90 ‘]‘
+ ‘[‘ 101 -ge 90 ‘]‘
+ ‘[‘ 101 -le 100 ‘]‘
+ tag=0
+ case $tag in
+ echo ‘The number range is 0-100.‘
The number range is 0-100.

[[email protected] shell]# sh -x  case1.sh
+ read -p ‘Please input a number: ‘ n
Please input a number: 78
+ ‘[‘ -z 78 ‘]‘
++ echo 78
++ sed ‘s/[0-9]//g‘
+ n1=
+ ‘[‘ -n ‘‘ ‘]‘
+ ‘[‘ 78 -lt 60 ‘]‘
+ ‘[‘ 78 -ge 60 ‘]‘
+ ‘[‘ 78 -lt 80 ‘]‘
+ tag=2
+ case $tag in
+ echo ok
ok

原文地址：http://blog.51cto.com/13517254/2105139