Shell scripting tutorial [7] - Shell test command

Shell scripting tutorial [7] - Shell test command

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Directory : https://blog.csdn.net/shn111/article/details/131590488

Reference tutorial : https://www.runoob.com/linux/linux-shell.html

Online editor : https://www.runoob.com/try/runcode.php?filename=helloworld&type=bash

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

numerical test

parameter	illustrate
-eq	true if equal to
- is	true if not equal
-gt	true if greater than
-ge	True if greater than or equal to
-lt	true if less than
- the	true if less than or equal to

Example:

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
# 两个数相等！

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[]Perform basic arithmetic operations in code

a=5
b=6

result=$[a+b] # 注意等号两边不能有空格
echo "result 为： $result"
# result 为： 11

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string test

parameter	illustrate
=	true if equal to
!=	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

Example:

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
# 两个字符串不相等!

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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

Example (tested in the online editor at the beginning of this article):

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

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In addition, the shell also provides and (-a) or (-o) not (!) Three logical operators are used to connect test conditions, and their priorities are: highest, second, !and -alowest -o. For example:

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
# 至少有一个文件存在!