sed: allow '0rFILE' (insert FILE before the first line)

The 'r' command can be used with address zero, effectively prepending
a file to the beginning of the input file, e.g.:
    sed '0rA.TXT' B.TXT > C.TXT
is equivalent to:
    cat A.TXT B.TXT > C.TXT

With "sed -i", this allows safe in-place prepending of files.
A typical example would be adding a license header to multiple source
files:
    sed -i '0rLICENSE' *.c *.h
    find -iname '*.cpp' | xargs sed -i '0rLICENSE'

A current cumbersome alternative is:
    sed -i -e 'x;${p;x};1rA.TXT' -e '1d'  B.TXT

* NEWS: Mention new feature.
* sed/sed.h (struct readcmd): New struct. (struct sed_cmd): Use new
struct instead of a char* for the filename.
* sed/compile.c (compile_program): Expand conditional detecting invalid
usage of "0" address to allow "0r"; Adjust '0r' to '1r' with prepending
(instead of appending).
* sed/execute.c (execute_program): 'r' command: support prepending.
* sed/debug.c (debug_print_function): Use the new 'struct readcmd'.
* testsuite/cmd-0r.sh: New test.
* testsuite/local.mk (TESTS): Add new test.
* doc/sed.texi (Zero Address): New section. (Adding a header to multiple
files): New example section.

1 files changed, 1 insertions, 1 deletions

diff --git a/sed/debug.c b/sed/debug.c
index 0530496..99f8b87 100644
--- a/sed/debug.c
+++ b/sed/debug.c
@@ -363,7 +363,7 @@ debug_print_function (const struct vector *program, const struct sed_cmd *sc)
 
     case 'r':
       putchar (' ');
-      fputs (sc->x.fname, stdout);
+      fputs (sc->x.readcmd.fname, stdout);
       break;
 
     case 'R':