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

colint has asked for the wisdom of the Perl Monks concerning the following question:

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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Comment on Why do I sometimes get null characters after the line feed when writing to files? Download Code

Replies are listed 'Best First'.
Re: Why do I sometimes get null characters after the line feed when writing to files? by dave_the_m (Monsignor) on Dec 18, 2006 at 16:20 UTC
The output doesn't contain a null character; its just an artifact of the way od displays contents in units of 2 bytes: `$ echo "ab" > /tmp/foo $ ls -l /tmp/foo -rw-r--r-- 1 davem davem 3 Dec 18 16:16 /tmp/foo $ od -xc /tmp/foo 0000000 6261 000a a b \n \0 0000003 $ echo "abc" > /tmp/foo $ ls -l /tmp/foo -rw-r--r-- 1 davem davem 4 Dec 18 16:17 /tmp/foo $ od -xc /tmp/foo 0000000 6261 0a63 a b c \n 0000004 $` [download] (Note that the first one is length three, but od displays a fourth null byte.) Dave.	[reply] [d/l]
Re: Why do I sometimes get null characters after the line feed when writing to files? by derby (Abbot) on Dec 18, 2006 at 16:17 UTC
I believe that's really an artifact of od when the input is an odd number of bytes. -derby	[reply]
Re: Why do I sometimes get null characters after the line feed when writing to files? by graff (Chancellor) on Dec 18, 2006 at 23:44 UTC
When I use a different set of options with "od", there is no problem: `$ echo ab \| od -cx # your method: 2-byte units in hex 0000000 a b \n + 6162 0a00 + 0000003 $ echo ab \| od -c -t xC # my method: char-sized units in hex 0000000 a b \n + 61 62 0a + 0000003` [download]	[reply] [d/l]