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3.6 Input and output
SINGULAR's input and output (short, I/O) are realized using links.
Links are the communication channels of SINGULAR, i.e., something
SINGULAR can write to and read from. In this section, a short
overview of the usage of links and of the different link types is given.
For loading of libraries, see LIB. For executing program scripts,
see filecmd.
Monitoring
A special form of I/O is monitoring. When monitoring is enabled,
SINGULAR makes a typescript of everything printed on your terminal
to a file. This is
useful to create a protocol of a SINGULAR session. The
monitor command enables and disables this feature
(see monitor).
How to use links
Recall that links are the communication channels of SINGULAR, i.e.,
something SINGULAR can write to and read from using the functions
write and read. There are furthermore
the functions dump and getdump which store resp.
retrieve the content of an entire SINGULAR session to, resp. from,
a link. The dump and getdump commands are not available
for DBM links.
For more information, see write, read, dump,
getdump.
Example:
| | ring r; poly p = x+y;
dump(":w test.sv"); // dump the session to the file test.sv
kill r; // kill the basering
listvar(); // no output after killing the ring
getdump(":r test.sv");// read the dump from the file
==> // ** redefining stdfglm (load("standard.lib","try");)
==> // ** redefining stdfglm (load("standard.lib","try");)
==> // ** redefining stdhilb (load("standard.lib","try");)
==> // ** redefining stdhilb (load("standard.lib","try");)
==> // ** redefining quotientList (load("standard.lib","try");)
==> // ** redefining quotientList (load("standard.lib","try");)
==> // ** redefining par2varRing (load("standard.lib","try");)
==> // ** redefining par2varRing (load("standard.lib","try");)
==> // ** redefining hilbRing (load("standard.lib","try");)
==> // ** redefining hilbRing (load("standard.lib","try");)
==> // ** redefining qslimgb (load("standard.lib","try");)
==> // ** redefining qslimgb (load("standard.lib","try");)
==> // ** redefining groebner (load("standard.lib","try");)
==> // ** redefining groebner (load("standard.lib","try");)
==> // ** redefining res (load("standard.lib","try");)
==> // ** redefining res (load("standard.lib","try");)
==> // ** redefining quot (load("standard.lib","try");)
==> // ** redefining quot (load("standard.lib","try");)
==> // ** redefining quot1 (load("standard.lib","try");)
==> // ** redefining quotient0 (load("standard.lib","try");)
==> // ** redefining quotient1 (load("standard.lib","try");)
==> // ** redefining quotient1 (load("standard.lib","try");)
==> // ** redefining quotient2 (load("standard.lib","try");)
==> // ** redefining quotient2 (load("standard.lib","try");)
==> // ** redefining quotient3 (load("standard.lib","try");)
==> // ** redefining quotient3 (load("standard.lib","try");)
==> // ** redefining quotient5 (load("standard.lib","try");)
==> // ** redefining quotient5 (load("standard.lib","try");)
==> // ** redefining quotient4 (load("standard.lib","try");)
==> // ** redefining quotient4 (load("standard.lib","try");)
==> // ** redefining intersect1 (load("standard.lib","try");)
==> // ** redefining sprintf (load("standard.lib","try");)
==> // ** redefining sprintf (load("standard.lib","try");)
==> // ** redefining printf (load("standard.lib","try");)
==> // ** redefining printf (load("standard.lib","try");)
==> // ** redefining fprintf (load("standard.lib","try");)
==> // ** redefining fprintf (load("standard.lib","try");)
==> // ** redefining weightKB (load("standard.lib","try");)
==> // ** redefining weightKB (load("standard.lib","try");)
==> // ** redefining datetime (load("standard.lib","try");)
==> // ** redefining datetime (load("standard.lib","try");)
==> // ** redefining kbclass (load("standard.lib","try");)
==> // ** redefining delkbclass (load("standard.lib","try");)
==> // ** redefining kbprepare (load("standard.lib","try");)
==> // ** redefining checkww (load("standard.lib","try");)
==> // ** redefining widkbase (load("standard.lib","try");)
==> // ** redefining weightmon (load("standard.lib","try");)
==> // ** redefining max (load("standard.lib","try");)
==> // ** redefining max (load("standard.lib","try");)
==> // ** redefining min (load("standard.lib","try");)
==> // ** redefining min (load("standard.lib","try");)
==> // ** redefining mod_init (load("standard.lib","try");)
listvar();
==> // r [0] *ring
==> // p [0] poly
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Specifying a link can be as easy as specifying a filename as a string.
Links do not even need to be explicitly opened
or closed before, resp. after, they are used. To explicitly open or
close a link, the open, resp. close, commands may be
used (see open, close).
Links have various properties which can be queried using the
status function (see status).
Example:
| | link l = "ssi:fork";
l;
==> // type : ssi
==> // mode : fork
==> // name :
==> // open : no
==> // read : not open
==> // write: not open
open(l);
status(l, "open");
==> yes
close(l);
status(l, "open");
==> no
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ASCII links
Data that can be converted to a string can be written into files for
storage or communication with other programs. The data are written in
plain ASCII format. Reading from an ASCII link returns a string ---
conversion into other data is up to the user. This can be done, for
example, using the command execute (see execute).
ASCII links should primarily be used for storing small amounts of data,
especially if it might become necessary to manually inspect or
manipulate the data.
See ASCII links, for more information.
Example:
| | // (over)write file test.ascii, link is specified as string
write(":w test.ascii", "int i =", 3, ";");
// reading simply returns the string
read("test.ascii");
==> int i =
==> 3
==> ;
==>
// but now test.ascii is "executed"
execute(read("test.ascii"));
i;
==> 3
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Ssi links
Data is communicated with other processes (e.g., SINGULAR
processes) which may run on the same computer or on different ones. Data
exchange is accomplished using TCP/IP links in the ssi format.
Reading from an ssi link returns the written expressions (i.e., not a
string, in general).
Ssi links should primarily be used for communicating with other
programs or for parallel computations (see, for example,
Parallelization with ssi links).
See Ssi links, for more information.
Example:
| | ring r;
link l = "ssi:tcp localhost:"+system("Singular"); // declare a link explicitly
open(l); // needs an open, launches another SINGULAR as a server
write(l, x+y);
kill r;
def p = read(l);
typeof(p); p;
==> poly
==> x+y
close(l); // shuts down SINGULAR server
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DBM links
Data is stored in and accessed from a data base. Writing is
accomplished by a key and a value and associates the value with the key
in the specified data base. Reading is accomplished w.r.t. a key,
the value associated to it is returned. Both the key and the value have to
be specified as strings. Hence, DBM links may be used only for data
which may be converted to or from strings.
DBM links should primarily be used when data needs to be accessed not in a
sequential way (like with files) but in an associative way (like with
data bases).
See DBM links, for more information.
Example:
| | ring r;
// associate "x+y" with "mykey"
write("DBM:w test.dbm", "mykey", string(x+y));
// get from data base what is stored under "mykey"
execute(read("DBM: test.dbm", "mykey"));
==> x+y
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