Perl sans frontiers

I often want to retrieve results from an external process within a Perl script. In theory, this is easy. All you need to do is something like...

$Result = `ls *.sql`

...which works perfectly well on any Unix (or Linux) system. The problem is that it doesn't work at all on Windows so, if you want your programme to be fully portable, you need a workaround. My solution is to use the one common feature on both Windows and Unix, the redirection character (>).

Say I want to run a SQL query (because this is something I do frequently, I have a subroutine for it)...

# =======================================
# Runs an SQL file, returning the result.
# ---------------------------------------
# $_[0] is the connection string.
# $_[1] is the file to run.
# $_[2] is a file to write the result to.
# ---------------------------------------
# (This last is necessary because the ``
# syntax does not work in Windows.)
# =======================================
sub RunSqlQuery
{
my $V_COMMAND = "sqlplus "
. $C_SQLPLUS_FLAGS
. " "
. $_[0]
." \@"
. $_[1]
. " >"
. $_[2];
my $V_RESULT;

# --------------------------------
# Run the command created above...
# --------------------------------
system $V_COMMAND;

# ---------------------------------
# Get the result back from the file
# and send it up the call chain...
# ---------------------------------
$V_RESULT = ReadResultFile $_[2];
return $V_RESULT;
}

Now the above piece of code will work, unaltered, on both Windows and Unix. Then all we need to get at the result is a matching sub-routine to read the file...

# ===============================================
# Reads a file in which a result has been placed.
# -----------------------------------------------
# $_[0] name of the file to read.
# -----------------------------------------------
# This is one of the workarounds made necessary
# because the syntax "VAR=`command`" does not
# work in Windows the same as it does in Unix.
# ===============================================
sub ReadResultFile
{
my $V_BUFFER;
open(H_SQL_FILE, "<$_[0]") or die "FAILURE: Cannot open " . $_[0];
read H_SQL_FILE, $V_BUFFER, 65535;
close H_SQL_FILE;
return $V_BUFFER;
}

The size limit of 65535 bytes is completely arbitrary and can be altered to meet the specific requirements of the application.
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