Notice the null character in the first example doesn't show up in the others. 
[predb24:~/tests] $ cat lines.pl
#!/usr/bin/perl
open (TEST, ">test.txt");
print TEST "This is a test\n";
#print TEST "This is a test\n";
#print TEST "";<br/>
close TEST;<br/>
[predb24:~/tests] $ lines.pl
[predb24:~/tests] $ od -cx test.txt
0000000   T   h   i   s       i   s       a       t   e   s   t  \n  \
+0
        6854 7369 6920 2073 2061 6574 7473 000a
0000017

[predb24:~/tests] $ cat lines.pl
#!/usr/bin/perl
open (TEST, ">test.txt");
print TEST "This is a test\n";
print TEST "This is a test\n";
#print TEST "";
close TEST;
[predb24:~/tests] $ lines.pl
[predb24:~/tests] $ od -cx test.txt
0000000   T   h   i   s       i   s       a       t   e   s   t  \n   
+T
        6854 7369 6920 2073 2061 6574 7473 540a
0000020   h   i   s       i   s       a       t   e   s   t  \n
        6968 2073 7369 6120 7420 7365 0a74
0000036

#!/usr/bin/perl
open (TEST, ">test.txt");
print TEST "This is a test\n";
print TEST "This is a test\n";
print TEST "";
close TEST;
[predb24:~/tests] $ lines.pl
[predb24:~/tests] $ od -cx test.txt
0000000   T   h   i   s       i   s       a       t   e   s   t  \n   
+T
        6854 7369 6920 2073 2061 6574 7473 540a
0000020   h   i   s       i   s       a       t   e   s   t  \n
        6968 2073 7369 6120 7420 7365 0a74
0000036

[predb24:~/tests] $ cat lines.pl
#!/usr/bin/perl
open (TEST, ">test.txt");
#print TEST "This is a test\n";
#print TEST "This is a test\n";
print TEST "\n";
close TEST;
[predb24:~/tests] $ lines.pl
[predb24:~/tests] $ od -cx test.txt
0000000  \n  \0
        000a
0000001

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In reply to Why do I sometimes get null characters after the line feed when writing to files? by colint

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