Fwd: input redirect from a variable

Fwd: input redirect from a variable

[Peter Stephenson]

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Message-Id: <pdy98830623095bbf58c3401e47@[192.168.1.2]>
Date: Thu, 22 Sep 2005 13:30:00 -0700
To: Peter Stephenson <pws@csr.com>
From: Dave Yost <Dave@Yost.com>
Subject: input redirect from a variable
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Hi.

It seems to me that there should be a way to do something like this:

foo1="$(...)"
foo2="$(...)"

comm -3 <<<<$foo1 <<<<$foo2

where the <<<$foo1 syntax says to output $foo1 to a tmp file, then 
use that filenamne as the argument, then delete that file.

Thanks

Dave


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Re: input redirect from a variable

[Mikael Magnusson]

On 9/23/05, Peter Stephenson <pws@csr.com> wrote:
>
> ------- Forwarded Message
>
> Mime-Version: 1.0
> Message-Id: <pdy98830623095bbf58c3401e47@[192.168.1.2]>
> Date: Thu, 22 Sep 2005 13:30:00 -0700
> To: Peter Stephenson <pws@csr.com>
> From: Dave Yost <Dave@Yost.com>
> Subject: input redirect from a variable
> Content-Type: text/plain; charset="us-ascii" ; format="flowed"
>
> Hi.
>
> It seems to me that there should be a way to do something like this:
>
> foo1="$(...)"
> foo2="$(...)"
>
> comm -3 <<<<$foo1 <<<<$foo2
>
> where the <<<$foo1 syntax says to output $foo1 to a tmp file, then
> use that filenamne as the argument, then delete that file.
>
> Thanks
>
> Dave

I use this function for comparing the hexdump of two files,
hexdiff () {
	diff -u <(hexdump "$1") <(hexdump "$2")
}

so in your case, what you want to do is comm -3 <(...) <(...)
or if you really want
foo1=$(...)
foo2=$(...)
comm -3 <(echo "$foo1") <(echo "$foo2")
but that seems stupid :)
Also note this syntax will provide pipes, if you use =(...) instead
you will get temp files like you asked for.

--
Mikael Magnusson

Re: input redirect from a variable

[Dave Yost]

Thanks.

<(foo) and =(foo) should be mentioned in the REDIRECTION section, where I would have found them.

Dave

At 12:15 PM +0200 2005-09-23, Mikael Magnusson wrote:
>On 9/23/05, Peter Stephenson <pws@csr.com> wrote:
>>
>> ------- Forwarded Message
>>
>> Mime-Version: 1.0
>> Message-Id: <pdy98830623095bbf58c3401e47@[192.168.1.2]>
>> Date: Thu, 22 Sep 2005 13:30:00 -0700
>> To: Peter Stephenson <pws@csr.com>
>> From: Dave Yost <Dave@Yost.com>
>> Subject: input redirect from a variable
>> Content-Type: text/plain; charset="us-ascii" ; format="flowed"
>>
>> Hi.
>>
>> It seems to me that there should be a way to do something like this:
>>
>> foo1="$(...)"
>> foo2="$(...)"
>>
>> comm -3 <<<<$foo1 <<<<$foo2
>>
>> where the <<<$foo1 syntax says to output $foo1 to a tmp file, then
>> use that filenamne as the argument, then delete that file.
>>
>> Thanks
>>
>> Dave
>
>I use this function for comparing the hexdump of two files,
>hexdiff () {
>	diff -u <(hexdump "$1") <(hexdump "$2")
>}
>
>so in your case, what you want to do is comm -3 <(...) <(...)
>or if you really want
>foo1=$(...)
>foo2=$(...)
>comm -3 <(echo "$foo1") <(echo "$foo2")
>but that seems stupid :)
>Also note this syntax will provide pipes, if you use =(...) instead
>you will get temp files like you asked for.
>
>--
>Mikael Magnusson

Re: input redirect from a variable

[Bart Schaefer]

On Sep 23,  6:14am, Dave Yost wrote:
} Subject: Re: input redirect from a variable
}
} <(foo) and =(foo) should be mentioned in the REDIRECTION section,

But they *aren't* redirections.

Redirection implies changing a file descriptor.  <(foo) and =(foo)
create file name strings and substitute them into the command line.

Re: input redirect from a variable

[Dave Yost]

At 2:21 PM +0000 2005-09-23, Bart Schaefer wrote:
>On Sep 23,  6:14am, Dave Yost wrote:
>} Subject: Re: input redirect from a variable
>}
>} <(foo) and =(foo) should be mentioned in the REDIRECTION section,
>
>But they *aren't* redirections.
>
>Redirection implies changing a file descriptor.  <(foo) and =(foo)
>create file name strings and substitute them into the command line.

Yes, you're right, now that I think of it.  But they should still be mentioned under redirections with a pointer to where to find them discussed.  (The use of "<" is a little confusing, too.)  Any shell user knows about redirection, but then when you imagine this new facility you want (as I did), you don't have a name for it, so redirection is the first place you look.

Dave

Re: input redirect from a variable

[Bart Schaefer]

On Sep 23, 12:15pm, Mikael Magnusson wrote:
}
} > foo1="$(...)"
} > foo2="$(...)"
} >
} > comm -3 <<<<$foo1 <<<<$foo2
} 
} comm -3 <(echo "$foo1") <(echo "$foo2")
} but that seems stupid :)

Incidentally:

    comm -3 =(<<<$foo1) =(<<<$foo2)

There already is a <<< syntax, but it turns a string into standard input
as a "here document".  Wrapping that in =(...) causes zsh to read that
input and put it in the temp file.

A nice optimization (which has not yet been done) would be to have this
special case avoid forking a new process, much as $(<file) reads a file.
Right now =(<<<...) is equivalent to =($NULLCMD <<<...).  Which actually
seems like a bug to me; shouldn't it use $READNULLCMD instead?  (Not that
one really wants "more" rather than "cat" inside a substitution, but even
outside of substitutions, here-documents are fed to $NULLCMD rather than
to $READNULLCMD.)

Re: input redirect from a variable

[Peter Stephenson]

Bart Schaefer wrote:
> A nice optimization (which has not yet been done) would be to have this
> special case avoid forking a new process, much as $(<file) reads a file.

This isn't too difficult since most of the hairy test for a simple
enough redirection already exists (and presumably works, though I
certainly can't tell by looking at it).

> Right now =(<<<...) is equivalent to =($NULLCMD <<<...).  Which actually
> seems like a bug to me; shouldn't it use $READNULLCMD instead?  (Not that
> one really wants "more" rather than "cat" inside a substitution, but even
> outside of substitutions, here-documents are fed to $NULLCMD rather than
> to $READNULLCMD.)

It's a bit curious, but maybe the thinking was that you aren't likely to
want to look at a here-doc or here-string via a pager, which is the
typical use of $READNULLCMD.

Index: Doc/Zsh/expn.yo
===================================================================
RCS file: /cvsroot/zsh/zsh/Doc/Zsh/expn.yo,v
retrieving revision 1.55
diff -u -r1.55 expn.yo
--- Doc/Zsh/expn.yo	2 Sep 2005 11:38:42 -0000	1.55
+++ Doc/Zsh/expn.yo	23 Sep 2005 16:40:08 -0000
@@ -340,6 +340,15 @@
 form for a program that expects to lseek (see manref(lseek)(2))
 on the input file.
 
+There is an optimisation for substitutions of the form
+tt(=LPAR()<<<)var(arg)tt(RPAR()), where var(arg) is a single-word argument
+to the here-string redirection tt(<<<).  This form produces a file name
+containing the value of var(arg) after any substitutions have been
+performed.  This is handled entirely within the current shell.  This is
+effectively the reverse of the special form tt($LPAR()<)var(arg)tt(RPAR())
+which treats var(arg) as a file name and replaces it with the file's
+contents.
+
 The tt(=) form is useful as both the tt(/dev/fd) and the named pipe
 implementation of tt(<LPAR())var(...)tt(RPAR()) have drawbacks.  In 
 the former case, some programmes may automatically close the file
Index: Src/exec.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/exec.c,v
retrieving revision 1.92
diff -u -r1.92 exec.c
--- Src/exec.c	8 Aug 2005 17:01:37 -0000	1.92
+++ Src/exec.c	23 Sep 2005 16:40:23 -0000
@@ -2941,33 +2941,50 @@
     return fd;
 }
 
-/* $(...) */
+/*
+ * Test if some wordcode starts with a simple redirection of type
+ * redir_type.  If it does, return the name of the file, copied onto
+ * the heap.  If it doesn't, return NULL.
+ */
 
-/**/
-LinkList
-getoutput(char *cmd, int qt)
+static char *
+simple_redir_name(Eprog prog, int redir_type)
 {
-    Eprog prog;
-    int pipes[2];
-    pid_t pid;
     Wordcode pc;
 
-    if (!(prog = parse_string(cmd)))
-	return NULL;
-
     pc = prog->prog;
     if (prog != &dummy_eprog &&
 	wc_code(pc[0]) == WC_LIST && (WC_LIST_TYPE(pc[0]) & Z_END) &&
 	wc_code(pc[1]) == WC_SUBLIST && !WC_SUBLIST_FLAGS(pc[1]) &&
 	WC_SUBLIST_TYPE(pc[1]) == WC_SUBLIST_END &&
 	wc_code(pc[2]) == WC_PIPE && WC_PIPE_TYPE(pc[2]) == WC_PIPE_END &&
-	wc_code(pc[3]) == WC_REDIR && WC_REDIR_TYPE(pc[3]) == REDIR_READ && 
+	wc_code(pc[3]) == WC_REDIR && WC_REDIR_TYPE(pc[3]) == redir_type &&
 	!WC_REDIR_VARID(pc[3]) &&
 	!pc[4] &&
 	wc_code(pc[6]) == WC_SIMPLE && !WC_SIMPLE_ARGC(pc[6])) {
+	return dupstring(ecrawstr(prog, pc + 5, NULL));
+    }
+
+    return NULL;
+}
+
+/* $(...) */
+
+/**/
+LinkList
+getoutput(char *cmd, int qt)
+{
+    Eprog prog;
+    int pipes[2];
+    pid_t pid;
+    char *s;
+
+    if (!(prog = parse_string(cmd)))
+	return NULL;
+
+    if ((s = simple_redir_name(prog, REDIR_READ))) {
 	/* $(< word) */
 	int stream;
-	char *s = dupstring(ecrawstr(prog, pc + 5, NULL));
 
 	singsub(&s);
 	if (errflag)
@@ -3101,6 +3118,7 @@
     char *nam;
     Eprog prog;
     int fd;
+    char *s;
 
     if (thisjob == -1)
 	return NULL;
@@ -3109,13 +3127,36 @@
     if (!(nam = gettempname(NULL, 0)))
 	return NULL;
 
+    if ((s = simple_redir_name(prog, REDIR_HERESTR))) {
+	/*
+	 * =(<<<stuff).  Optimise a la $(<file).  It's
+	 * effectively the reverse, converting a string into a file name
+	 * rather than vice versa.
+	 */
+	singsub(&s);
+	if (errflag)
+	    s = NULL;
+	else
+	    untokenize(s);
+    }
+
     if (!jobtab[thisjob].filelist)
 	jobtab[thisjob].filelist = znewlinklist();
     zaddlinknode(jobtab[thisjob].filelist, nam);
 
-    child_block();
+    if (!s)
+	child_block();
     fd = open(nam, O_WRONLY | O_CREAT | O_EXCL | O_NOCTTY, 0600);
 
+    if (s) {
+	/* optimised here-string */
+	int len;
+	unmetafy(s, &len);
+	write(fd, s, len);
+	close(fd);
+	return nam;
+    }
+
     if (fd < 0 || (cmdoutpid = pid = zfork(NULL)) == -1) {
 	/* fork or open error */
 	child_unblock();
Index: Test/A04redirect.ztst
===================================================================
RCS file: /cvsroot/zsh/zsh/Test/A04redirect.ztst,v
retrieving revision 1.9
diff -u -r1.9 A04redirect.ztst
--- Test/A04redirect.ztst	16 Apr 2005 23:24:57 -0000	1.9
+++ Test/A04redirect.ztst	23 Sep 2005 16:40:24 -0000
@@ -269,3 +269,11 @@
   exec {myfd}>&-
 1:Error closing file descriptor using readonly variable
 ?(eval):4: can't close file descriptor from readonly parameter myfd
+
+# This tests the here-string to filename optimisation; we can't
+# test that it's actually being optimised, but we can test that it
+# still works.
+  cat =(<<<$'This string has been replaced\nby a file containing it.\n')
+0:Optimised here-string to filename
+>This string has been replaced
+>by a file containing it.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
Cambridge, CB4 0WZ, UK                          Tel: +44 (0)1223 692070


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