Re: printf '%s\n' "$@" versus <<< redirection

[alex xmb ratchev]

On Sat, Feb 18, 2023, 1:52 PM Kerin Millar <kfm@plushkava.net> wrote:

> On Sat, 18 Feb 2023 13:21:48 +0100
> alex xmb ratchev <fxmbsw7@gmail.com> wrote:
>
> > may i ask for what the IFS= does in a single var read ment ?
> > i know its been manywhere , but , i couldnt keep it
>
> (It wasn't easy to pick out your response)
>
> The default value of IFS is $' \t\n'. This affects how word splitting
> works and how read splits a line into fields (it follows the same rules as
> for word splitting). The manual has this to say:-
>
> "If IFS is unset, or its value is exactly <space><tab><newline>, the
> default, then sequences of <space>, <tab>, and <newline> at the beginning
> and end of the results of the previous expansions are ignored, and any
> sequence of IFS characters not at the beginning or end serves to delimit
> words."
>
> Pay particular attention to the observation that a consecutive sequence of
> any of those three characters at the beginning and end of the results are
> ignored. We can see exactly that happening in the following example.
>
> $ printf ' \t \t this is\tmy line \t \t ' | { read -r line; echo "${line@Q}";
> }
> $'this is\tmy line'
>
> The manual goes on to say, "If the value of IFS is null, no word splitting
> occurs." We can prove this by putting it to the test.
>
> $ printf ' \t \t this is\tmy line \t \t ' | { IFS= read -r line; echo
> "${line@Q}"; }
> ' \t \t this is\tmy line \t \t '
>
> In summary, if reading to one variable name, the default value of IFS
> causes leading and trailing sequences of <space> and <tab> to be removed.
> Setting IFS as empty prevents splitting and causes read to assign to the
> _first_ specified variable name, with the original content of the line not
> being modified in any way. In the latter case, if you specify more than one
> variable name, the second onwards will only end up being empty.


i see , i wasnt aware of such importantness , .. deserves much bigger
tension .. IFS= needed for 1:1 data preservance , ..
thank u much for your kind answer

-- 
> Kerin Millar
>