[9fans] Making read(1) an rc(1) builtin?

[pmarin.mail@gmail.com (pmarin)]

Write some real world  tests using bash/GNU tools, rc (with static
linked versions of p9p)  and tell us what happend.
Maybe you will be surprised.

[1] http://cm.bell-labs.com/cm/cs/tpop/

On Mon, Apr 4, 2011 at 12:30 AM,  <smiley at zenzebra.mv.com> wrote:
> I'm in the process of writing some filters in rc(1). ?One thing that has
> come to concern me about rc(1) is that read(1) is not a "builtin"
> command. ?For example, with a loop like:
>
> ? ?while(message=`{read})
> ? ? ?switch($message) {
> ? ? ?case foo
> ? ? ? ?dofoo
> ? ? ?case bar
> ? ? ? ?dobar
> ? ? ?case *
> ? ? ? ?dodefault
> ? ? ?}
>
> Each line that's read by the script causes it to fork a new process,
> /bin/read, whose sole purpose is to read a single line and die. ?That
> means at least one fork for each line read and, if your input has many
> lines, that means spawning many processes. ?I wonder if it wouldn't make
> sense to move read(1) into rc(1) and make it a "builtin" command. ?A
> wrapper script could then be created, at /bin/read, to call "rc -c 'eval
> read $*'" with the appropriate arguments (or sed $n^q, etc.), for any
> program that requires an actual /bin/read to exist.
>
> A similar line of thought holds for /bin/test. ?The string and numeric
> tests (-n, -z, =, !=, <, >, -lt, -eq, -ne, etc.) can be very frequently
> used, and can lead to spawning unnecessarily many processes. ?For the
> file test parameters (-e, -f, -d, -r, -x, -A, -L, -T, etc.), however,
> this argument isn't as strong. ?Since the file tests have to stat(2) a
> path, they already require a call to the underlying file system, and an
> additional fork wouldn't be that much more expensive. ?I could see the
> string and numeric tests being moved into rc(1) as a "test" builtin,
> with the file tests residing at "/bin/ftest" (note the "f"). ?The "test"
> builtin could scan its arguments and call "ftest" if needed. ?A wrapper
> script at /bin/test could provide compatibility for existing programs
> which expect an executable named /bin/test to exist.
>
> I understand the Unix/Plan 9 philosophy of connecting tools that do one
> job and do it well. ?But I don't think /bin/read and /bin/test are
> places where that philosophy is practical (i.e., efficient). ?After all,
> reading input lines really is the perogative of any program that
> processes line-oriented data (like rc(1) does). ?In addition, /bin/read
> represents a simple and fairly stable interface that's not likely to
> change appreciably in the future. ?Comparison of numeric and string
> values is also a fairly stable operation that's not likely to change,
> and is not likely to be needed outside of rc(1). ?Most programming
> languages (C, awk, etc.) have their own mechanisms for integer and
> string comparison. ?I suspect moving these operations into rc(1) (with
> appropriate replacement scripts to ensure compatibility) could
> appreciably increase the performance of shell scripts, with very little
> cost in modularity or compatibility.
>
> Any thoughts on this?
>
> I'm also a bit stumped by the fact that rc(1) doesn't have anything
> analogous to bash(1)'s string parsing operations: ${foo#bar},
> ${foo##bar}, ${foo%bar}, ${foo%%bar}, or ${foo/bar/baz}. ?Is there any
> way to extract substrings (or single characters) from a string in rc(1)
> without having to fork a dd, awk, or sed? ?I've tried setting ifs='' and
> using foo=($"bar), but rc(1) always splits bar on spaces. ?Perhaps, if
> rc(1) used the first character of $ifs to split $"bar, $bar could be
> split into individual characters when ifs=''. ?Then, the characters of
> $bar could be addressed without resort to dd and friends.
>
> (As a side note, if anyone goes into rc(1)'s source to implement any of
> this, please add a "--" option (or similar) to the "echo" builtin while
> you're there. ?Having to wrap echo in:
>
> ? ?# make 'myecho $foo' work even when $foo starts with '-n'
> ? ?fn myecho {
> ? ? ?if(~ $1 --) {
> ? ? ? ?shift
> ? ? ? ?if(~ $1 -n) {
> ? ? ? ? ?shift
> ? ? ? ? ?echo -n -n $*
> ? ? ? ? ?echo
> ? ? ? ?}
> ? ? ? ?if not echo $*
> ? ? ?}
> ? ? ?if not echo $*
> ? ?}
>
> can be rather inconvenient.)
>
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