Common file test operations in Perl

Performing an action based on the existence or contents of a file or directory is fairly common in shell scripting. In this article, we explore some of the tests that we can run against a file/directory using the if conditional statement.

1. Check for existence of file (-e).

The following little program checks if a file named testfile exists & prints the name else it prints the error message stored in $! variable.

#!/usr/bin/perl -w
#
use strict ;

my $file_name = "/root/testfile";

if (-e $file_name) {
        print "file name is $file_name \n" ;
}
else {
        print "$file_name $! \n" ;
}

When we execute the script we get the following result:

[root@alive ~]# ./filetest.pl

file name is /root/testfile

Now if I change the file name to testfile1, the output changes.

[root@alive ~]# ./filetest.pl

/root/testfile1 No such file or directory

2. Check if file is writable (-w).

3. Check if file is empty (-z):

The file testfile is not empty, so if I run the following script:

#!/usr/bin/perl -w

#

use strict ;

my $file_name = "/root/testfile";

if (-z $file_name) {

        print "file name is $file_name \n" ;

}

else {

        print "$file_name not empty $! \n" ;

}

I'll get this result:

[root@alive ~]# ./filetest.pl

/root/testfile not empty

[root@alive ~]#

We can run negate tests as well, For example if I wanted a true result from if statement if the file was not empty, I could precede -z by not to indicate a negative match as shown below:

#!/usr/bin/perl -w

#

use strict ;

my $file_name = "/root/testfile";

if (not -z $file_name) {

        print "file name is $file_name \n" ;

}

else {

        print "$file_name not empty $! \n" ;

The result of this scripts' execution would be:

[root@alive ~]# ./filetest.pl

file name is /root/testfile

4. Check if the file is a plain text file (-f).

This will check if the file is a text file or a special file like a device file or an executable file.

5. Check that the file exists and is of non-zero size (-s).

This can be regarded as somewhat the opposite of the -z option.

6. Check if the file is a directory (-d).

There are many more file test operations available which can be looked up from perldoc.