8、Shell运算符：Shell算数运算符、关系运算符、布尔运算符、字符串运算符等

#!/bin/bash
val=`expr 2 + 2`
echo "Total value : $val"

Total value : 4

#!/bin/sh

a=10
b=20
val=`expr $a + $b`
echo "a + b : $val"

val=`expr $a - $b`
echo "a - b : $val"
val=`expr $a \* $b`
echo "a * b : $val"

val=`expr $b / $a`
echo "b / a : $val"

val=`expr $b % $a`
echo "b % a : $val"
if [ $a == $b ]
then
echo "a is equal to b"
fi

if [ $a != $b ]
then
echo "a is not equal to b"
fi

a + b : 30
a - b : -10
a * b : 200
b / a : 2
b % a : 0
a is not equal to b

#!/bin/sh

a=10
b=20
if [ $a -eq $b ]
then
echo "$a -eq $b : a is equal to b"
else
echo "$a -eq $b: a is not equal to b"
fi

if [ $a -ne $b ]
then
echo "$a -ne $b: a is not equal to b"
else
echo "$a -ne $b : a is equal to b"
fi
if [ $a -gt $b ]
then
echo "$a -gt $b: a is greater than b"
else
echo "$a -gt $b: a is not greater than b"
fi
if [ $a -lt $b ]
then
echo "$a -lt $b: a is less than b"
else
echo "$a -lt $b: a is not less than b"
fi

if [ $a -ge $b ]
then
echo "$a -ge $b: a is greater or equal to b"
else
echo "$a -ge $b: a is not greater or equal to b"
fi

if [ $a -le $b ]
then
echo "$a -le $b: a is less or equal to b"
else
echo "$a -le $b: a is not less or equal to b"
fi

10 -eq 20: a is not equal to b
10 -ne 20: a is not equal to b
10 -gt 20: a is not greater than b
10 -lt 20: a is less than b
10 -ge 20: a is not greater or equal to b
10 -le 20: a is less or equal to b

#!/bin/sh

a=10
b=20

if [ $a != $b ]
then
echo "$a != $b : a is not equal to b"
else
echo "$a != $b: a is equal to b"
fi

if [ $a -lt 100 -a $b -gt 15 ]
then
echo "$a -lt 100 -a $b -gt 15 : returns true"
else
echo "$a -lt 100 -a $b -gt 15 : returns false"
fi
if [ $a -lt 100 -o $b -gt 100 ]
then
echo "$a -lt 100 -o $b -gt 100 : returns true"
else
echo "$a -lt 100 -o $b -gt 100 : returns false"
fi

if [ $a -lt 5 -o $b -gt 100 ]
then
echo "$a -lt 100 -o $b -gt 100 : returns true"
else
echo "$a -lt 100 -o $b -gt 100 : returns false"
fi

10 != 20 : a is not equal to b
10 -lt 100 -a 20 -gt 15 : returns true
10 -lt 100 -o 20 -gt 100 : returns true
10 -lt 5 -o 20 -gt 100 : returns false

#!/bin/sh

a="abc"
b="efg"

if [ $a = $b ]
then
echo "$a = $b : a is equal to b"
else
echo "$a = $b: a is not equal to b"
fi

if [ $a != $b ]
then
echo "$a != $b : a is not equal to b"
else
echo "$a != $b: a is equal to b"
fi

if [ -z $a ]
then
echo "-z $a : string length is zero"
else
echo "-z $a : string length is not zero"
fi
if [ -n $a ]
then
echo "-n $a : string length is not zero"
else
echo "-n $a : string length is zero"
fi

if [ $a ]
then
echo "$a : string is not empty"
else
echo "$a : string is empty"
fi

abc = efg: a is not equal to b
abc != efg : a is not equal to b
-z abc : string length is not zero
-n abc : string length is not zero
abc : string is not empty

#!/bin/sh

file="/var/www/tutorialspoint/unix/test.sh"

if [ -r $file ]
then
echo "File has read access"
else
echo "File does not have read access"
fi
if [ -w $file ]
then
echo "File has write permission"
else
echo "File does not have write permission"
fi
if [ -x $file ]
then
echo "File has execute permission"
else
echo "File does not have execute permission"
fi
if [ -f $file ]
then
echo "File is an ordinary file"
else
echo "This is sepcial file"
fi
if [ -d $file ]
then
echo "File is a directory"
else
echo "This is not a directory"
fi

if [ -s $file ]
then
echo "File size is zero"
else
echo "File size is not zero"
fi

if [ -e $file ]
then
echo "File exists"
else
echo "File does not exist"
fi

File has read access
File has write permission
File has execute permission
File is an ordinary file
This is not a directory
File size is zero
File exists