Re: bash "while do echo" can't function correctly

[Greg Wooledge]

On Wed, Apr 13, 2016 at 01:43:42PM +0100, Stephane Chazelas wrote:
> 2016-04-13 08:10:15 +0200, Geir Hauge:
> [...]
> >     while read -r line; do echo "$line"; done < test.txt
> > 
> > though printf should be preferred over echo:
> > 
> >     while read -r line; do printf '%s\n' "$line"; done < test.txt
> [...]
> 
> Actually, you also need to empty $IFS
> 
> while IFS= read -r line; do printf '%s\n' "$line"; done < test.txt

That will preserve every full line of input (except for the NUL bytes),
including leading and trailing spaces.

If you actually *want* the leading and trailing IFS whitespace characters
to be trimmed (the default behavior of read), then do it Geir's way.  In
many cases, that's desired.

> And if you want to keep eventual spurious characters after the
> last NL character in the file:
> 
> while IFS= read -r line; do printf '%s\n' "$line"; done < test.txt
> [ -z "$line" ] || printf %s "$line"

Another way to write that is:

while IFS= read -r line || [[ $line ]]; do ... done < test.txt