Getting Started with Shell Scripting-9

Shell test command

The test command in the Shell is used to check whether a certain condition is established, and it can perform three tests of numerical value, character and file.

Numerical test

parameter	illustrate
-eq	equal to true
-born	not equal to true
-gt	greater than true
-give	true if greater than or equal to
-lt	true if less than
-the	true if less than or equal to

Case:

num1=100
num2=100
if test $[num1] -eq $[num2]
then
    echo '两个数相等！'
else
    echo '两个数不相等！'
fi

输出结果：两个数相等！

 The [] in the code performs basic arithmetic operations , such as:

#!/bin/bash
a=5
b=6
result=$[a+b] # 注意等号两边不能有空格
echo "result 为： $result"

结果为:result 为： 11

String test

parameter	illustrate
=	equal to true
!=	true if not equal
-z string	True if the length of the string is zero
-n string	True if the length of the string is not zero

Case:

num1="ru1noob"
num2="runoob"
if test $num1 = $num2
then
    echo '两个字符串相等!'
else
    echo '两个字符串不相等!'
fi

输出结果：两个字符串不相等!

file test

parameter	illustrate
-e filename	true if the file exists
-r filename	True if the file exists and is readable
-w filename	True if the file exists and is writable
-x filename	True if the file exists and is executable
-s filename	True if the file exists and has at least one character
-d filename	true if the file exists and is a directory
-f filename	true if the file exists and is a normal file
-c filename	True if the file exists and is a character special file
-b filename	True if the file exists and is a block special file

Case:

cd /bin
if test -e ./bash
then
    echo '文件已存在!'
else
    echo '文件不存在!'
fi

输出结果：文件已存在!

In addition, Shell also provides and (-a) , or (-o) , not (!) three logical operators used to connect test conditions , the priority is: "!" highest, "-a" times In other words, "-o" is the lowest . E.g:

cd /bin
if test -e ./notFile -o -e ./bash
then
    echo '至少有一个文件存在!'
else
    echo '两个文件都不存在'
fi

输出结果：至少有一个文件存在!