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

[goncholden]

------- Original Message -------
On Monday, February 20th, 2023 at 4:32 AM, Kerin Millar <kfm@plushkava.net> 
wrote:


> On Sun, 19 Feb 2023 16:25:13 +0000
> goncholden goncholden@protonmail.com wrote:
> 
> > ------- Original Message -------
> > On Sunday, February 19th, 2023 at 3:17 AM, Greg Wooledge greg@wooledge.org 
> > wrote:
> > 
> > > On Sat, Feb 18, 2023 at 10:46:08AM +0000, goncholden wrote:
> > > 
> > > > My intention is to use prinf line by line on arguments containing 
> > > > newlines. With a newline also introduced between arguments $1 $2 $3 etc.
> > > 
> > > This is quite unique. I don't believe I've ever seen someone try to
> > > write a command where each argument is a group of lines, and all of
> > > the groups of lines are supposed to be concatenated together to form
> > > one bigger group of lines.
> > > 
> > > For this goal, printf '%s\n' "$@" seems to be the correct choice.
> > > 
> > > The <<< "$@" construct is nonsensical. Whatever it does (which is
> > > pretty hard to predict, since it doesn't have a real definition), it
> > > will not serve your goal.
> > > 
> > > If you want to avoid a pipeline which would cause your processing loop
> > > to run in a subshell, then your syntax of choice would be:
> > > 
> > > while read ...
> > > do
> > > ...
> > > done < <(printf '%s\n' "$@")
> > 
> > I have found that nested loops are most clear Consequently, I have either 
> > this one
> > 
> > Code:
> > 
> > # Loop over arguments
> > for arg in "$@"; do
> > # Loop over lines
> > printf '%s\n' "$arg" |
> > while IFS= read -r vl ; do
> > ...
> > done
> > done
> > 
> > or this
> > 
> > Code:
> > 
> > # Loop over arguments
> > for arg in "$@"; do
> > # Loop over lines
> > while IFS= read -r vl ; do
> > ...
> > done < <(printf '%s\n' "$arg")
> > done
> 
> 
> The use of a process substitution - as in your second example - is typical in 
> bash because, by having the while command be run in the initial shell, it's 
> immune to the issue of 'disappearing' variables. See 
> https://mywiki.wooledge.org/BashFAQ/024 for further details. Whether that 
> truly matters in your case depends on what "..." is exactly.
> 
> --
> Kerin Millar

One purpose is to pass documentation information with colour designators for 
consecutive lines.


var1="
Blue:
-h, --help
  Prints help.
Green:
  For more details see section 3." 

var2="
Examples
Blue:
  theone -d DIR
White:
  Transfers files to directory DIR"

thefunc "var1" "var2"