Shell Programming and Scripting

vger99 has the syntax. But the direction you are taking seems to be wrong. A fd is specific to a process. Exporting a vaiable containing an fd is senseless. In your first post, when you said "function", I assumed you meant "function". A function is ksh concept and it can have locally scoped variables. A global variable is global to the script, not the environment.

First of all, vger99, thank you. This will solve the problem that I was struggling with. I was probably wrapping myself around my own axils pretty tight because I did double up the "$" symbols, however, I was escaping the second rather than the first. Thanks again.

Secondly, Perderabo, I don't really prefer the direction I am taking either but, considering the fact that I am trying to fit this into my existing library of functions, I think that this may be acceptable. I am also considering an array (three arrays perhaps because of KSH-88) that will help me find the fds.

I'll explain the concept further to clear it up; perhaps you have a better suggestion. Judging from the examples that I have seen with your name attached, I am sure you can come up with something more elegant.

a. I have existing functions to communicate to my co-process, lets call them func_write and func_read.
b. Within these functions, I currently communicate to my co-process with print -p and read -p.
c. I want to eliminate the need to disconnect from my current database so I can communication to a new database for some sporadic lookups.
d. I thought that I could create two co-processes (hence requiring the I/O redirection) and define file descriptors for each co-process.
e. Therefore, to keep my current functions generic, I thought that I would supply a database descriptor (handle) to each function (e.g. func_write "something" database_handle_1)
f. Within the function, I would translate "database_handle_1" into a variable that was previously exported so that I can retrieve the correct fd and then use print -u${database_handle_1_stdout}

Arrays will give me the same thing but referencing dynamic variables seemed logial when I started thinking through how to implement this.

Thanks again,

Thomas

In item "f"; why do you suddenly start talking about exported variables? export makes a variable available to child processes. Those children will have their own fd's. Take at look at this:

Code:

#! /usr/bin/ksh

X=2

function one
{
        typeset X
        X=7
        echo in one X = $X
        return
}

function two
{
        X=9
        echo in two X = $X
        return
}
echo before one X = $X
one
echo before two X = $X
two
echo final X = $X
exit 0

Note that there is no "export". However there is a global variable called X. The function called "two" uses this global variable. The function called "one", while it uses a variable called X, it is a local X, not the global X.

When it run it, I get:
before one X = 2
in one X = 7
before two X = 2
in two X = 9
final X = 9

Thanks for pointing that out. I understand the scope of the variables with regards to the functions and exporting the variables is overkill; you are correct. I really want global variables; my thought process was clouded by my "eval" issues.

I have a (now) working proof of concept but I would still like to hear your thoughts on improving the concept.

Code:

#!/usr/bin/ksh

function connect
{
    typeset x=$1
    typeset o=$2
    typeset i=$3

    printf "\nFunction connect()\n"

    sqlplus -s /nolog |&

    eval "${x}_stdout=${o}"
    eval "${x}_stdin=${i}"

    STDOUT=$(eval "print \$${x}_stdout")
    STDIN=$(eval "print \$${x}_stdin")

    eval "exec ${STDOUT}>&p"
    eval "exec ${STDIN}<&p"

    if [ ${x} = "TEST1" ]
    then
        eval "print -u${STDOUT} \"connect USER_A/PWD_A@DB1\""
    else
        eval "print -u${STDOUT} \"connect USER_B/PWD_B@DB2\""
    fi
    eval "read -u${STDIN} LINE"
    print "From sqlplus: $LINE"
}

function test_comm
{
    typeset x=$1

    printf "\nFunction test_comm()\n"

    STDOUT=$(eval "print \$${x}_stdout")
    STDIN=$(eval "print \$${x}_stdin")

    eval "print -u${STDOUT} \"SHOW USER\""
    eval "read -u${STDIN} LINE"
    print "From sqlplus: $LINE"
}

ps -ef | grep sqlplus | grep -v grep
connect TEST1 3 4
connect TEST2 5 6

ps -ef | grep sqlplus | grep -v grep
test_comm TEST1
test_comm TEST2
test_comm TEST1
test_comm TEST2

Now here are the results:

Function connect()
From sqlplus: Connected.

Function connect()
From sqlplus: Connected.

me 8118 8106 0 13:51:00 pts/6 0:00 sqlplus -s /nolog
me 8113 8106 0 13:51:00 pts/6 0:00 sqlplus -s /nolog

Function test_comm()
From sqlplus: USER is "USER_A"

Function test_comm()
From sqlplus: USER is "USER_B"

Function test_comm()
From sqlplus: USER is "USER_A"

Function test_comm()
From sqlplus: USER is "USER_B"

The results are what I want and I will use some other kind of global variable to track and define fds so "o" and "i" in connect() won't really exist when implemented.

Thanks again,

Thomas