I've been doing some research on how to correctly read lines from a file whose last line may not have a trailing newline character. Have found the answer in Read a line-oriented file which may not end with a newline.
However, I have a second goal that is to exclude the comments at the beginning of lines and have found a grep command that achieves the goal
$ grep -v '^ *#' file
But I have noticed that this command has a (for me unexpected) side behavior: it adds a trailing newline character in the last line if it does not exist
$ cat file
# This is a commentary
aaaaaa
# This is another commentary
bbbbbb
cccccc
$ od -c file
0000000 # T h i s i s a c o m m
0000020 e n t a r y \n a a a a a a \n #
0000040 T h i s i s a n o t h e r
0000060 c o m m e n t a r y \n b b b b b
0000100 b \n c c c c c c \n
0000111
$ truncate -s -1 file
$ od -c file
0000000 # T h i s i s a c o m m
0000020 e n t a r y \n a a a a a a \n #
0000040 T h i s i s a n o t h e r
0000060 c o m m e n t a r y \n b b b b b
0000100 b \n c c c c c c
0000110
$ od -c <(grep -v '^ *#' file)
0000000 a a a a a a \n b b b b b b \n c c
0000020 c c c c \n
0000025
Notice that besides removing the line beginning comments it also adds a trailing newline character in the last line.
How could that be?
