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Linux Basic Tutorial

Linux Reference Manual

Shell test Command

The test command in Shell is used to check if a condition is true, it can perform tests on numbers, characters, and files.

numeric test

Parameter Description
-eq equal then true
-ne not equal is true
-gt greater than is true
-ge greater than or equal to is true
-lt less than is true
-le less than or equal to is true
num1=100
num2=100
if test $[num1]　-eq $[num2]
then
　　　　echo 'Two numbers are equal!'
else
　　　　echo 'Two numbers are not equal!'
fi

Output Result:

Two numbers are equal!

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

#!/bin/bash
a=5
b=6
result=$[a+b] # Note that there should be no space around the equal sign
echo "result is: $result"

The result is:

result is:　11

string test

Parameter Description
= equal then true
!== not equal then true
-z string The length of the string is zero if true
-n String If the length of the string is not zero, it is true
num1="ru1noob"
num2="w3codebox"
if test $num1　= $num2
then
　　　　echo 'Two strings are equal!'
else
　　　　echo 'Two strings are not equal!'
fi

Output Result:

Two strings are not equal!

File Test

Parameter Description
-e Filename If the file exists, it is true
-r Filename If the file exists and is readable, it is true
-w Filename If the file exists and is writable, it is true
-x Filename If the file exists and is executable, it is true
-s Filename If the file exists and has at least one character, it is true
-d Filename If the file exists and is a directory, it is true
-f Filename If the file exists and is a regular file, it is true
-c Filename If the file exists and is a character special file, it is true
-b Filename If the file exists and is a block special file, it is true
cd　/bin
if test　-e ./bash
then
　　　　echo 'File already exists!'
else
　　　　echo 'File does not exist!'
fi

Output Result:

File already exists!

In addition, Shell also provides with ( -a ) Or ( -o ) Non-(! ) three logical operators are used to connect test conditions, with their priority as: ! highest, -a Next, -o Lowest. For example:

cd　/bin
if test　-e ./notFile　-o　-e ./bash
then
　　　　echo 'At least one file exists!'
else
　　　　echo 'Two files do not exist'
fi

Output Result:

At least one file exists!
Shell Flow ControlShell printf Command