Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!mcvax!unido!gmdzi!tietz
From: tietz@gmdzi.UUCP (Christoph Tietz)
Newsgroups: comp.sources.bugs
Subject: the adventure of sed to perl conversion
Keywords: perl, sed, conversion
Message-ID: <836@gmdzi.UUCP>
Date: 12 Sep 88 16:24:30 GMT
Article-I.D.: gmdzi.836
Organization: GMD, Sankt Augustin, F. R. Germany
Lines: 75

For the last few hours I tried to convert my sed scripts for the
postprocessing of automatically generated makefiles to perl scripts.
I use perl 2.0 patchlevel 14. In principle perl really is a GREAT tool
and I think I will rewrite a lot of my shell scripts to perl scripts.
Nevertheless the conversion of my sed scripts to perl led to some problems
that I want to state here. Perhaps some kind guru can enlighten me on
the nature of my problems ?

A problem with the different notion of line ends in sed and perl could
easily be solved. s2p translates the sed expression:

	#   second case: no '\' at line end => append '\' to line end and
	#		 insert .sym dependency as new line without '\'
	#		 at the end
	#
	s/^\(\([^ \	]*\)_Dummy\.o:.*[^\\]\)$/\1 \\\
	\	\	\2\.sym/

to:

	s/^(([^ \	]*)_Dummy\.o:.*[^\\])$/$1 \\\n\	\	$2\.sym/;

This is not what was intended, because '$1' in the perl script contains the
whole line including the newline character and the match perl performs
allows a backslash at the end of the line because the newline character is
matched against [^\\]. Because of this the perl substitution just inserts
a new line that contains a space and the backslash even if the matching
line ends with '\'. I had to change the perl command to:

    if (/^([^ \	]*)_Dummy\.o:.*[^\\]\n$/) {
       chop; $_ .= "\\\n";
       $atext .= "\	\	$1.sym \n";
    }
    # print $_ and $atext

and it worked. My first question: Why is the '\n' before the line end '$'
neccessary ? What sense makes the existence of '$' if I have to use '\n' to
anchor a match at the line end ? What possibility do I have to end a line
other than using '\n' as the delimiter ?

The next problem took me more time to solve. s2p translates:

		/^[^ ]*\.out:/,/^[ ]*$/d

to the perl command:

	if (/^[^ ]*\.out:/ .. /^[ ]*$/) {
	   # skip this input line
	}

The sed script is intended to clean up a makefile that contains the lines:

SIMCore_Dummy.out: SIMCore_Dummy.o UserCore.o /users/susi/vaxlib/Strings.o 
		$(M2C) -e SIMCore_Dummy -o \
		SIMCore_Dummy.out $(M2FLAGS) $(M2LINK) 

objects: 	Alias.sym Alias.o CoreTool.sym CoreTool.o Env.sym Env.o \

The sed script erases the lines from "SIMCore_Dummy.out:" up to the line
before "objects:". The perl script erases the whole file following
"SIMCore_Dummy.out:". The end of the range is never found. If the range
expression is evaluated before the 'IF' statement everything works fine:

    $gotcha = /^[^ ]*\.out:/ .. /^[ ]*$/;
    if ($gotcha) { 
       # skip this input line
    }

does exactly what I wanted it to do. My second question: Is this a bug or
am I missing some semantical details?

Thank you in advance for all responses.

    Christoph Tietz          (    tietz@gmdzi.uucp     )
                             ( or tietz@zix.gmd.dbp.de )