Shell file test operator | Examples

  table of Contents

One, the file test operator

2. Common examples

2.1 -d file detection directory 

2.2 -f file detects ordinary files

2.3 -x file detect file executable

2.4 -e file detects the existence of a file/directory

2.5 -b file detects block device files

Three, summary

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In Shell programming, the file test operator is widely used, and it is often necessary to detect the attributes of a file, which will be explained with examples below.

One, the file test operator

Table 1 File test operator table

Operator	Description
-b file	Check whether the file is a block device file, and return true if it is.
-c file	Check whether the file is a character device file, and return true if it is.
-d file	Check whether the file is a directory, and return true if it is.
-f file	Check whether the file is a normal file (neither a directory nor a device file), and return true if it is.
-g file	Check whether the SGID bit is set in the file, and return true if it is.
-in the file	Check whether the SUID bit is set in the file, and return true if it is.
-k file	Check whether the file has a sticky bit (Sticky Bit), if so, return true.
-p file	Check whether the file is a well-known pipe, and return true if it is.
-r file	Check if the file is readable, and return true if it is.
-w file	Check whether the file is writable, and return true if it is.
-x file	Check if the file is executable, and return true if it is.
-s file	Check whether the file is empty (whether the file size is greater than 0), return true if it is not empty.
-e file	Check whether the file (including directory) exists, and if so, return true.

2. Common examples

2.1 -d file detection directory 

#!/bin/bash

file="/root"
if [ -d $file ]
then
    echo "$file is directory!"
else
    echo "$file is not directory!"
fi

Output:

[root@localhost Shell]# ./dir.sh 
/root is directory!
[root@localhost Shell]#

2.2 -f file detects ordinary files

#!/bin/bash

file="/root/regularFile"
if [ -f $file ]
then
    echo "$file is regular file!"
else
    echo "$file is not regular file!"
fi

Output:

[root@localhost Shell]# ./dir.sh 
/root/regularFile is regular file!
[root@localhost Shell]#

2.3 -x file detect file executable

#!/bin/bash

file="/root/Shell/dir.sh"
if [ -x $file ]
then
    echo "$file is executable file!"
else
    echo "$file is not executable file!"
fi

Output:

[root@localhost Shell]# ls -l dir.sh 
-rwxr-xr-x. 1 root root 145 2月   6 10:54 dir.sh
[root@localhost Shell]# ./dir.sh 
/root/Shell/dir.sh is executable file!
[root@localhost Shell]#

2.4 -e file detects the existence of a file/directory

#!/bin/bash

file="/root"
if [ -e $file ]
then
    echo "$file is exist!"
else
    echo "$file is not exist!"
fi

Output:

[root@localhost Shell]# ./dir.sh 
/root is exist!
[root@localhost Shell]#

2.5 -b file detects block device files

#!/bin/bash

if [ -b /dev/sda ]
then
    echo "/dev/sda is Block Device File!"
else
    echo "/dev/sda is not Block Device File!"
fi

The output is:

[root@localhost Shell]# ./dir.sh 
/dev/sda is Block Device File!
[root@localhost Shell]#

Three, summary

File test operators are often used in Shell programming, and several commonly used operators should be remembered.

references:

[1] https://www.cnblogs.com/GyForever1004/p/8457028.html