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Top Forums UNIX for Dummies Questions & Answers exec command and field descriptors.. Post 58924 by Perderabo on Saturday 4th of December 2004 04:02:16 PM
Old 12-04-2004
The trouble is that exec can do several different things...it really needs to be several commands. The code you gave won't work. Change that to
exec $fd < inputfile
and it probably will. But that is not what's meant by an fd.

A fd is always an integer. In shell scripts, it will be a very low integer. By convention:
0 = standard input
1 = standard output
2 = standard error output

The idea is that you write your program to output to fd 1 without knowing what fd one is. Then at execution time you can do stuff like:
echo this > first.file
echo that > second.file

It would be terrible if echo always sent stuff to "first.file". You would need to do:
echo that
cp first.file second.file
or something like that.

By default 0 1 2 are all connected to /dev/tty so you can type input to a program and see the results in your window.

Here is an experiment I just did:
$ expr 1 + 2
3
$ expr 1 + 2 > expr.out
$ cat expr.out
3
$ expr cat + dog > expr.out
expr: non-numeric argument
$

With the last expr command, I have an error. Since the error goes to 2 which is still /dev/tty, I see it immediately, even though the standard which is 1 goes to a file. That why we have both 1 and 2. You can send 1 into a file while 2 is still displayed to you.

Don't want to see error messages? Bad idea usually, but you can do:
expr cat + dog > expr.out 2>/dev/null

And now error messages are thrown away.

expr cat + dog > expr.out
really means
expr cat + dog 1> expr.out
but if you leave the integer off, 1 is assumed for > while 0 is assumed for <
 

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SQL::Translator::Parser::SQLite(3pm)			User Contributed Perl Documentation		      SQL::Translator::Parser::SQLite(3pm)

NAME
SQL::Translator::Parser::SQLite - parser for SQLite SYNOPSIS
use SQL::Translator; use SQL::Translator::Parser::SQLite; my $translator = SQL::Translator->new; $translator->parser("SQL::Translator::Parser::SQLite"); DESCRIPTION
This is a grammar for parsing CREATE statements for SQLite as described here: http://www.sqlite.org/lang.html CREATE INDEX sql-statement ::= CREATE [TEMP | TEMPORARY] [UNIQUE] INDEX index-name ON [database-name .] table-name ( column-name [, column-name]* ) [ ON CONFLICT conflict-algorithm ] column-name ::= name [ ASC | DESC ] CREATE TABLE sql-command ::= CREATE [TEMP | TEMPORARY] TABLE table-name ( column-def [, column-def]* [, constraint]* ) sql-command ::= CREATE [TEMP | TEMPORARY] TABLE table-name AS select-statement column-def ::= name [type] [[CONSTRAINT name] column-constraint]* type ::= typename | typename ( number ) | typename ( number , number ) column-constraint ::= NOT NULL [ conflict-clause ] | PRIMARY KEY [sort-order] [ conflict-clause ] | UNIQUE [ conflict-clause ] | CHECK ( expr ) [ conflict-clause ] | DEFAULT value constraint ::= PRIMARY KEY ( name [, name]* ) [ conflict-clause ]| UNIQUE ( name [, name]* ) [ conflict-clause ] | CHECK ( expr ) [ conflict-clause ] conflict-clause ::= ON CONFLICT conflict-algorithm CREATE TRIGGER sql-statement ::= CREATE [TEMP | TEMPORARY] TRIGGER trigger-name [ BEFORE | AFTER ] database-event ON [database-name .] table-name trigger-action sql-statement ::= CREATE [TEMP | TEMPORARY] TRIGGER trigger-name INSTEAD OF database-event ON [database-name .] view-name trigger-action database-event ::= DELETE | INSERT | UPDATE | UPDATE OF column-list trigger-action ::= [ FOR EACH ROW | FOR EACH STATEMENT ] [ WHEN expression ] BEGIN trigger-step ; [ trigger-step ; ]* END trigger-step ::= update-statement | insert-statement | delete-statement | select-statement CREATE VIEW sql-command ::= CREATE [TEMP | TEMPORARY] VIEW view-name AS select-statement ON CONFLICT clause conflict-clause ::= ON CONFLICT conflict-algorithm conflict-algorithm ::= ROLLBACK | ABORT | FAIL | IGNORE | REPLACE expression expr ::= expr binary-op expr | expr like-op expr | unary-op expr | ( expr ) | column-name | table-name . column-name | database-name . table-name . column-name | literal-value | function-name ( expr-list | * ) | expr (+) | expr ISNULL | expr NOTNULL | expr [NOT] BETWEEN expr AND expr | expr [NOT] IN ( value-list ) | expr [NOT] IN ( select-statement ) | ( select-statement ) | CASE [expr] ( WHEN expr THEN expr )+ [ELSE expr] END like-op::= LIKE | GLOB | NOT LIKE | NOT GLOB AUTHOR
Ken Youens-Clark <kclark@cpan.org>. SEE ALSO
perl(1), Parse::RecDescent, SQL::Translator::Schema. perl v5.14.2 2012-01-18 SQL::Translator::Parser::SQLite(3pm)
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