The shell builtin command test can be used to check file types and compare expressions value. The syntax is test EXPRESSION or the test command is also equivalent to [ EXPRESSION ].
It returns the exit code 1 (false) if the EXPRESSION result is 0, and 0 (true) for a non-zero EXPRESSION result.
If no EXPRESSION is provided, the exit status is set to 1 (false).
Different kinds of checks can be done on the file using the test command; for example, file existence test, directory test, regular file check, symbolic link check, and so on.
The options available to do various checks on a file are explained in the following table:
|
Option |
Description |
|---|---|
|
-e |
fileChecks whether the file exists |
|
-f file |
The file is a regular fil |
|
-d file |
The file exists and is a directory |
|
-h, -L file |
The file is a symbolic link |
|
-b file |
The file is block special |
|
-c file |
The file is character special |
|
-S file |
The file is a socket |
|
-p file |
The file is a named pipe |
|
-k file |
Sticky bit of the file is set |
|
-g file |
set-group-ID (sgid) bit of the file is set |
|
-u file |
set-user-id (suid) bit of the file is set |
|
-r file |
Read permission on the file exists |
|
-w file |
Write permission on the file exists |
|
-x file |
Execute permission on the file exists |
|
-t fd |
File descriptor fd is open on terminal |
|
file1 -ef file2 |
file1 is hard link to file2 |
|
file1 -nt file2 |
file1 is more recent compared to file2 |
|
file1 -ot file2 |
The modification time of file1 is older than file2 |
Shell script performs different checks on the files as follows:
#!/bin/bash # Filename: file_checks.sh # Description: Performing different check on and between files # Checking existence of /tmp/file1 echo -n "Does File /tmp/file1 exist? " test -e /tmp/file1 echo $? # Create /tmp/file1 touch /tmp/file1 /tmp/file2 echo -n "Does file /tmp/file1 exist now? " test -e /tmp/file1 echo $? # Check whether /tmp is a directory or not echo -n "Is /tmp a directory? " test -d /tmp echo $? # Checking if sticky bit set on /tmp" echo -n "Is sticky bit set on /tmp ? " test -k /tmp echo $? # Checking if /tmp has execute permission echo -n "Does /tmp/ has execute permission ? " test -x /tmp echo $? # Creating another file /tmp/file2 touch /tmp/file2 # Check modification time of /tmp/file1 and /tmp/file2 echo -n "Does /tmp/file1 modified more recently than /tmp/file2 ? " test /tmp/file1 -nt /tmp/file2 echo $?
The output of running this script is as follows:
Does File /tmp/file1 exist? 1 Does file /tmp/file1 exist now? 0 Is /tmp a directory? 0 Is sticky bit set on /tmp ? 0 Does /tmp/ has execute permission? 0 Does /tmp/file1 modified more recently than /tmp/file2 ? 1
In our output, 0 and 1 are the exist status after running a test command on files. The output 1 means the test failed and 0 means the test was successfully passed.
We can also perform arithmetic checks between integer numbers. Comparison possible on integers is explained to following table:
|
Comparison |
Description |
|---|---|
|
|
INTEGER1 is equal to INTEGER2 |
|
|
INTEGER1 is not equal to INTEGER2 |
|
|
INTEGER1 is greater than INTEGER2 |
|
|
INTEGER1 is greater than or equal to INTEGER2 |
|
|
INTEGER1 is lesser than INTEGER2 |
|
|
INTEGER1 is lesser than or equal to INTEGER2 |
Shell script shows various arithmetic checks between two integers as follows:
#!/bin/bash # Filename: integer_checks.sh # Description: Performing different arithmetic checks between integers a=12 b=24 c=78 d=24 echo "a = $a , b = $b , c = $c , d = $d" echo -n "Is a greater than b ? " test $a -gt $b echo $? echo -n "Is b equal to d ? " test $b -eq $d echo $? echo -n "Is c not equal to d ? " test $c -ne $d echo $?
The output of running this script is as follows:
a = 12 , b = 24 , c = 78 , d = 24 Is a greater than b ? 1 Is b equal to d ? 0 Is c not equal to d ? 0
Also, here the test returns the exit status after running a comparison test between integers, and returns 0 (true) on success and 1 (false) if the test fails.
A command test also allows you to perform checks on and between strings. The possible checks are described in the following table:
|
Comparison |
Description |
|---|---|
|
|
The length of the string is zero |
|
|
The length of the string is non-zero |
|
|
STRING1 and STRING2 are equal |
|
|
STRING1 and STRING2 are not equal |
Shell script shows various string checks on and between strings as follows:
#!/bin/bash # Filename: string_checks.sh # Description: Performing checks on and between strings str1="Hello" str2="Hell" str3="" str4="Hello" echo "str1 = $str1 , str2 = $str2 , str3 = $str3 , str4 = $str4" echo -n "Is str3 empty ? " test -z $str3 echo $? echo -n "Is str2 not empty? " test -n $str2 echo $? echo -n "Are str1 and str4 equal? " test $str1 = $str4 echo $? echo -n "Are str1 and str2 different? " test $str1 != $str2 echo $?
The output of running this script is as follows:
str1 = Hello , str2 = Hell , str3 = , str4 = Hello Is str3 empty ? 0 Is str2 not empty? 0 Are str1 and str4 equal? 0 Are str1 and str2 different? 0
Here, the test returns 0 exit status if the string checks are true, else returns 1.
The test command also allows you to perform checks on and between expressions. An expression itself can contain multiple expressions to evaluate as well. The possible checks done are explained in the following table:
|
Comparison |
Description |
|---|---|
|
|
This EXPRESSION is true |
|
|
This EXPRESSION is false |
|
|
Both the expressions are true (the AND operation) |
|
|
Either one of the expressions is true (the OR operation) |
Shell script shows various string checks on and between strings as follows:
#!/bin/bash # Filename: expression_checks.sh # Description: Performing checks on and between expressions a=5 b=56 str1="Hello" str2="Hello" echo "a = $a , b = $b , str1 = $str1 , str2 = $str2" echo -n "Is a and b are not equal, and str1 and str2 are equal? " test ! $a -eq $b -a $str1 = $str2 echo $? echo -n "Is a and b are equal, and str1 and str2 are equal? " test $a -eq $b -a $str1 = $str2 echo $? echo -n "Does /tmp is a sirectory and execute permission exists? " test -d /tmp -a -x /tmp echo $? echo -n "Is /tmp file is a block file or write permission exists? " test -b /tmp -o -w /tmp echo $?
The output of running this script is as follows:
a = 5 , b = 56 , str1 = Hello , str2 = Hello Is a and b are not equal, and str1 and str2 are equal? 0 Is a and b are equal, and str1 and str2 are equal? 1 Does /tmp is a sirectory and execute permission exists? 0 Is /tmp file is a block file or write permission exists? 0
Similar to other checks with the test command, the 0 exit code means the expression evaluated is true and 1 means false evaluation.