Command Execution

>> the command printf seems to be ignoring the ending '\n' that passes to
>> it:
>>
>> [...]
>
> It's an interaction between the echo command and the shell that's
> causing the trailing \n to be removed. Printf is working just fine: $
> printf "hello\n" | od -t x1 -
> 0000000 68 65 6c 6c 6f 0a
> 0000006
> This is the correct output. But what happens when you use echo: $ echo
> -n `printf "hello\n\n\n\n\n"` | od -t x1 - 0000000 68 65 6c 6c 6f
> 0000005

oh, thanks for the input. It really made me thinking, and I found that it is not echo's fault, because the previous \n was printed ok. here is more test:

$ echo -n "`printf "hello\n\n"`" | od -t x1 -
0000000 68 65 6c 6c 6f
0000005

but:

$ echo -n "`printf "hello\n\n "`" | od -t x1 -
0000000 68 65 6c 6c 6f 0a 0a 20
0000010

So is it bash that is eating the trailing \n's?

> Avoid using "echo" when you need trailing whitespace; instead, write the

Actually, I use echo as an example, the assignment variable is then used in awk. :-) I need to get the result into a variable.

thanks

T

ps, my bash

$ bash --version
GNU bash, version 2.05b.0(1)-release (i386-pc-linux-gnu)

> So is it bash that is eating the trailing \n's?

Yes, but it's not a bug. See the section about “Command Substitution” in the bash(1) man page.

Matthew R. Dempsky

> Yes, but it's not a bug.  See the section about ``Command Substitution''
> in the bash(1) man page.

Got it:

,-----
| Bash performs the expansion by executing command and replacing the
| command substitution with the standard output of the command, with any
| trailing newlines deleted.  Embedded newlines are not deleted.
`-----

the "feature" is so confusing.

T

> the "feature" is so confusing.

It's so that shell snippets like

cd /lib/modules/`uname -r`/build

work correctly without extra hassle.

Matthew R. Dempsky