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Posted by howa on June 1, 2008, 2:41 pm
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Hi,
I have a SQL file (generated by mysql), it is over 2GB in size and its
few lines are:
cat -n test.sql
1 -- MySQL dump 8.23
2 --
3 ...
4 ...
Now, I have a program to read the file line by line:
#!/usr/bin/perl
use strict;
if ( scalar(@ARGV) == 1 ) {
my $filename = ( $ARGV[0] );
open(IN_FILE, $filename) or die("Could not open the file.");
my $line;
foreach $line (<IN_FILE>) {
print "Test";
exit;
}
close(IN_FILE);
}
Suppose the file will read the first line and exit, however, it was
halt and eating my memory forever, no output for print "Test" or exit
at all.
Any idea?
Howard.
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Posted by A. Sinan Unur on June 1, 2008, 2:52 pm
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f40ba0c2bfd2@y22g2000prd.googlegroups.com:
> Now, I have a program to read the file line by line:
No you don't.
> my $line;
>
> foreach $line (<IN_FILE>) {
Using a for loop here will read the entire file into memory first, before
it can begin to process the lines.
Instead, use a while loop which will indeed read the file line-by-line:
while ( my $line = <IN_FILE> ) {
Sinan
--
(remove .invalid and reverse each component for email address)
comp.lang.perl.misc guidelines on the WWW:
http://www.rehabitation.com/clpmisc/
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Posted by Jürgen Exner on June 1, 2008, 3:27 pm
Please log in for more thread options >Now, I have a program to read the file line by line:
>
> foreach $line (<IN_FILE>) {
But you don't. You are creating a list of all the lines in the file,
then looping through that list.
You are probably looking for
while (my $line= <IN_FILE>) {
jue
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Posted by howa on June 1, 2008, 10:19 pm
Please log in for more thread options Hi,
On 6=D4=C22=C8=D5, =C9=CF=CE=E73=95r27=B7=D6, J=A8=B9rgen Exner <jurge...@ho=
tmail.com> wrote:
> >Now, I have a program to read the file line by line:
>
> > foreach $line (<IN_FILE>) {
>
> But you don't. You are creating a list of all the lines in the file,
> then looping through that list.
>
> You are probably looking for
> while (my $line=3D <IN_FILE>) {
>
> jue
Oh..., I google for "perl read file line by line" and return "http://
www.cs.cf.ac.uk/Dave/PERL/node241.html", I overlooked the code in that
page are not reading line by line in fact!
Thanks guys!
Howard
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Posted by Uri Guttman on June 2, 2008, 12:17 am
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h> Oh..., I google for "perl read file line by line" and return "http://
h> www.cs.cf.ac.uk/Dave/PERL/node241.html", I overlooked the code in that
h> page are not reading line by line in fact!
that web page is purported to be a book (dunno if a dead tree version
was printed) but it is up there with the other crappy web tutorials out
there. i wish i had the resources to catalog and critique them. so many
to choose from.
this one is very idiosyncratic with short pages with weak examples and
even worse and wrong explanations.
from:
http://www.cs.cf.ac.uk/Dave/PERL/node23.html#SECTION00411000000000000000
You define scalar variables by assigning a value (number or
string) to it.
hmm. that seems to mean my $foo is not defining (really declaring) a scalar.
* It is a good idea to declare all variables together near the
top of the program.
that is actually backwards.
and nothing is mentioned about all the other scalar value types in this
page. in fact this page is more about the values than about the title
'scalar variables'. the author doesn't seem to know the difference
between the container and its contents.
from: http://www.cs.cf.ac.uk/Dave/PERL/node24.html
String Scalar Variables
that page title is so wrong.
from:
http://www.cs.cf.ac.uk/Dave/PERL/node27.html
Literal Arrays
Arrays can be defined literally in Perl code by simply enclosing
the array elements in parentheses and separating each array
element with a comma.
For example
(1, 2, 3)
("fred", "albert")
() # empty array (zero elements)
wow. i can't even begin to comment on that balderdash. i have never
heard of the term literal array (we call them lists). don't you love
technical authors who invent new terms instead of using the well known
and accepted ones?
from:
http://www.cs.cf.ac.uk/Dave/PERL/node20.html#SECTION00322100000000000000
Example: Back-Quoted Strings
It might be argued that back-quoted strings are not really a
data type. That's because Perl uses back-quoted strings to
execute system commands. When Perl sees a back-quoted string, it
passes the contents to Windows, UNIX, or whatever operating
system you are using.
hmm. the author doesn't seem to realize that backticks also are double
quoted strings and are literals in that sense. the fact that they shell
out is a secondary effect.
Let's see how to use the back-quoted string to display a
directory listing of all text files in the perl5 directory:
print `dir *.txt`;
wow, a useless example given readdir and glob!
from:
http://www.cs.cf.ac.uk/Dave/PERL/node60.html#SECTION00910000000000000000
$refFunction = \&function; & is a function location.
hmm. that calls the function ref. no location is returned.
of course he calls the tr/// op a regular expression. this is almost
universal in bad web tutes.
from:
http://www.cs.cf.ac.uk/Dave/PERL/node87.html#SECTION001180000000000000000
The binding operators (=~ and !~) are used as search, modify,
and translation operations and work on the $_ variable by
default.
actually if you use a bind op you DON'T default to operating on $_ but
on the bound value. wow.
from:
http://www.cs.cf.ac.uk/Dave/PERL/node81.html#SECTION001140000000000000000
The =~ lets you match against a specified target (rather than an
environment variable $_. In CGI (see Later) and other
application we frequently need to match against input
name/values.
this is even wackier. $_ is an environment variable? what is he smoking?
and why does he have 2 pages covering =~?
from:
http://www.cs.cf.ac.uk/Dave/PERL/node79.html#SECTION001121000000000000000
The control characters \d (digit), \s (space), \w (word
character) can also be used. \D, \S, \W are the negations of
\d\s\w (More on This Soon)
control characters??
ok, i had my fun. this is definitely the work of a dedicated author who
has never had anyone else comment on his work. i say this to my
students, job candidates, hiring clients, etc.: become part of the perl
community as you will learn more, gain valuable feedback and actually be
able to contribute something useful. writing (code or docs) in isolation
is never going to turn out well.
uri
--
Uri Guttman ------ uri@stemsystems.com -------- http://www.sysarch.com --
----- Perl Code Review , Architecture, Development, Training, Support ------
--------- Free Perl Training --- http://perlhunter.com/college.html ---------
--------- Gourmet Hot Cocoa Mix ---- http://bestfriendscocoa.com ---------
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