Re: Need detail: backslash-newline sequences inside of single-quoted strings

[gk]

At 01:10 PM 2/24/2006, Paul D. Smith wrote:
> Yes, that documentation was reworked and moved.  I'll update the NEWS
> file.
>
> Look in the chapter "Writing the Commands in Rules", section "Command
> Syntax", sub-section "Splitting Command Lines".

Thanks.
I think the examples are a bit hard to follow (at least in how 'info' 
formats it) - confused somewhat by the fact that the example itself is 
indented from normal flow of paragraph text.

I hope my email preserves enough white space to illustrate what I'm trying 
to say: I have replace tabs with spaces here, just to be clear - use 'info 
make' to see exactly what I'm referring to.

The general rule says:

>If the first character of the next line after the
backslash-newline is a tab, then that tab (and only that tab) is
removed.
...

THE FIRST EXAMPLE IS VERY CLEAR

-- EXAMPLE1 START --
   For example, this makefile:

     all :
             @echo no\
     space
             @echo no\
             space
[...]
consists of four separate shell commands where the output is:

     nospace
     nospace
[...]

-- EXAMPLE1 END--

THE ABOVE EXAMPLE ESTABLISHES THESE CONVENTIONS:
1. The position of 'all :' defines the limit of the 'pseudo left margin' / 
terminal output of the example (5 spaces from left of the true document margin)
2. A tab is represented by 8 SPACES: horizontal distance from 'all' to 
indented next line, '@echo'
3. The 'pseudo left margin' of example output is in line with the vertical 
position established by 'all :'


THIS EXAMPLE IS A BIT HARD TO FOLLOW

-- EXAMPLE2 START --
As a more complex example, this makefile:

     all : ; @echo 'hello \
             world' ; echo "hello \
         world"

will run one shell with a command script of:

     echo 'hello \
     world' ; echo "hello \
         world"
-- EXAMPLE2 INTERRUPTED--

MY COMMENT:

This seems fine to here - though a bit obscure:  I hope readers will be 
able to infer the difference between 8 SPACES representing a TAB (removed 
by make) and 4 spaces (preserved by make) as representing 4 SPACES (4 
spaces is a common TAB length too).

It might be helpful to make note of these conventions at the start of the 
discussion.

-- EXAMPLE2 CONTINUED--

which, according to shell quoting rules, will yield the following
output:

     hello \
     world
     hello     world

Notice how the backslash/newline pair was removed inside the string
quoted with double quotes (`"..."'), but not from the string quoted
with single quotes (`'...'').  This is the way the default shell
[...]
-- EXAMPLE2 END--

I think it would help to make note of my observations by re-wording the 
final paragraph to more clearly emphasize how the original rule was 
interpreted by make - how the shell translates the interpreted rule into 
output is less important to explain since most users will understand this.

SUGGESTED REVISION:

Notice what happened:

1. the backslash/newline pair inside the string with single quotes was 
preserved by make and preserved by the shell, in final output
2. the tab character at the beginning of the second line of the string 
inside single quotes was removed by make (as always), since it immediately 
follows a backslash/newline pair
3.  the backslash/newline pair inside the string with double quotes was 
preserved by make but interpreted as an escape sequence by the shell, in 
final output
4. the 4 spaces at the beginning of the second line of the string inside 
double quotes was preserved by make and preserved by the shell, in final output


- Greg Keraunen
http://www.xmake.org