Unix / Linux - Shell File Test Operators Example

Quiz

We have a few operators that can be used to test various properties associated with a Unix file.

Assume a variable file holds an existing file name "test" the size of which is 100 bytes and has read, write and execute permission on −

Operator	Description	Example
-b file	Checks if file is a block special file; if yes, then the condition becomes true.	[ -b $file ] is false.
-c file	Checks if file is a character special file; if yes, then the condition becomes true.	[ -c $file ] is false.
-d file	Checks if file is a directory; if yes, then the condition becomes true.	[ -d $file ] is not true.
-f file	Checks if file is an ordinary file as opposed to a directory or special file; if yes, then the condition becomes true.	[ -f $file ] is true.
-g file	Checks if file has its set group ID (SGID) bit set; if yes, then the condition becomes true.	[ -g $file ] is false.
-k file	Checks if file has its sticky bit set; if yes, then the condition becomes true.	[ -k $file ] is false.
-p file	Checks if file is a named pipe; if yes, then the condition becomes true.	[ -p $file ] is false.
-t file	Checks if file descriptor is open and associated with a terminal; if yes, then the condition becomes true.	[ -t $file ] is false.
-u file	Checks if file has its Set User ID (SUID) bit set; if yes, then the condition becomes true.	[ -u $file ] is false.
-r file	Checks if file is readable; if yes, then the condition becomes true.	[ -r $file ] is true.
-w file	Checks if file is writable; if yes, then the condition becomes true.	[ -w $file ] is true.
-x file	Checks if file is executable; if yes, then the condition becomes true.	[ -x $file ] is true.
-s file	Checks if file has size greater than 0; if yes, then condition becomes true.	[ -s $file ] is true.
-e file	Checks if file exists; is true even if file is a directory but exists.	[ -e $file ] is true.

Example

The following example uses all the file test operators −

Assume a variable file holds an existing file name "/var/www/tutorialspoint/unix/test.sh" the size of which is 100 bytes and has read, write and execute permission −

#!/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 not zero"
else
   echo "File size is zero"
fi

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

The above script will produce the following result −

File does not have write permission
File does not have execute permission
This is sepcial file
This is not a directory
File size is not zero
File does not exist

The following points need to be considered while using file test operators −

There must be spaces between the operators and the expressions. For example, 2+2 is not correct; it should be written as 2 + 2.
if...then...else...fi statement is a decision-making statement which has been explained in the next chapter.

unix-basic-operators.htm

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