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From: Decare on 8 Mar 2010 08:55
The following two commands have different effect.

$ echo A${IFS}B
A B

$ echo "A${IFS}B"
A
B

It is obvious that the first one interprets `IFS' as
space, while the second interprets it as new line.
In fect, the `IFS' represents three characters, namely
space, tab, and new line. why different choices occur
in different situations?

--
ego cogito ergo sum
From: pk on 8 Mar 2010 08:59
Decare wrote:

> The following two commands have different effect.
>
> $ echo A${IFS}B
> A B
>
> $ echo "A${IFS}B"
> A
> B
>
> It is obvious that the first one interprets `IFS' as
> space, while the second interprets it as new line.
> In fect, the `IFS' represents three characters, namely
> space, tab, and new line. why different choices occur
> in different situations?

It's not like you think. There's no "interpretation" whatsoever, only normal
shell operation. Run the output through "od -c":

$ echo A${IFS}B | od -c
0000000 A B \n
0000004
$ echo "A${IFS}B" | od -c
0000000 A \t \n B \n
0000006

Hint: when using double quotes, word splitting does not happen.
From: mop2 on 8 Mar 2010 10:15
On Mon, 08 Mar 2010 10:55:54 -0300, Decare <decare(a)yeah.net> wrote:

> The following two commands have different effect.
>
> $ echo A${IFS}B
> A B
>
> $ echo "A${IFS}B"
> A
> B
>
> It is obvious that the first one interprets `IFS' as
> space, while the second interprets it as new line.
> In fect, the `IFS' represents three characters, namely
> space, tab, and new line. why different choices occur
> in different situations?
>

As already said, your question is not about the variable "IFS",
but about the command "echo":

$ A=$'A\tB\nC D\n\n'
$ echo "$A"
A B
C D


$ echo $A
A B C D
$ echo "$A"
A B
C D


$
From: Dominic Fandrey on 8 Mar 2010 10:17
On 08/03/2010 14:55, Decare wrote:
> The following two commands have different effect.
>
> $ echo A${IFS}B
> A B
>
> $ echo "A${IFS}B"
> A
> B
>
> It is obvious that the first one interprets `IFS' as
> space,

IFS is appropriately interpreted, by the shell, however, \t
and \n are control characters, so the shell removes them,
because they are not protected by quotes.

--
A: Because it fouls the order in which people normally read text.
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A: Top-posting.
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From: Janis Papanagnou on 8 Mar 2010 10:19
mop2 wrote:
> On Mon, 08 Mar 2010 10:55:54 -0300, Decare <decare(a)yeah.net> wrote:
>
>> The following two commands have different effect.
>>
>> $ echo A${IFS}B
>> A B
>>
>> $ echo "A${IFS}B"
>> A
>> B
>>
>> It is obvious that the first one interprets `IFS' as
>> space, while the second interprets it as new line.
>> In fect, the `IFS' represents three characters, namely
>> space, tab, and new line. why different choices occur
>> in different situations?
>>
>
> As already said, your question is not about the variable "IFS",
> but about the command "echo":

No, it has nothing to do with the echo command (or builtin).
It's about word splitting, as pk already said.

Janis

>
> $ A=$'A\tB\nC D\n\n'
> $ echo "$A"
> A B
> C D
>
>
> $ echo $A
> A B C D
> $ echo "$A"
> A B
> C D
>
>
> $
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