using variables as strings in perl

Elukyz · 06-15-2007, 06:18 PM

Hello, i've recently begun learning perl and have came to an issue is where when I use a variable a new line is printed right after it...Example...

Code:

Quote:

#!/usr/bin/perl -w

#==========================================================
# Last updated: June 11, 2007
# NOTE TO SELF: ALL code blocks finish with ;
#==========================================================

######## Variables #######
my $myname = `whoami`;

####### Start of main script #######
print "Hello $myname, how are you doing today?\n";

Output from that code is as follows...
Hello Ike
, how are you doing today?

However, if I add an escape character before variable the string prints out as expected....

Quote:

#!/usr/bin/perl -w

#==========================================================
# Last updated: June 11, 2007
# NOTE TO SELF: ALL code blocks finish with ;
#==========================================================

#>>>>>>> Variables <<<<<<<
my $myname = `whoami`;

#>>>>>>> Start of main script <<<<<<<
print "Hello \$myname, how are you doing today?\n";

output:
Name "main::myname" used only once: possible typo at ./myperl.pl line 9.
Hello $myname, how are you doing today?
-end of output-

Can you help me find what it is that I am missing?

EDIT:
Left out the resource I am using for learning perl ...
site name: http://perldoc.perl.org/

wjevans_7d1@yahoo.co · 06-15-2007, 06:48 PM

First, I don't think the string prints out as expected when you escape the dollar sign, does it?

I mean, you want the result of whoami to be printed, but what you're getting is the string:

Quote:

$myname

itself.

So get rid of that escape character before the dollar sign, because you want the content of variable $myname, not the variable name itself.

Well, you want most of the content, anyway.

The result of the backtick quotes is to execute the command and place the output in variable $myname. But the output includes a line feed at the end. So you want to get rid of that.

Try this. I just tried it myself and it works just fine:

Code:

#!/usr/bin/perl

$myname=`whoami`;
chomp($myname);
print "Hello, $myname, how are you doing today?\n"

(I put the comma after Hello because my mother was an English teacher, and she brought me up right.)

Hope this helps.

rtspitz · 06-15-2007, 06:49 PM

the output of $myname = `whoami`; contains the username + \n at the end !
that's why a new line is started.

you can get rid of it with a substitition based on "regular expressions" like this:

Code:

#!/usr/bin/perl -w

#==========================================================
# Last updated: June 11, 2007
# NOTE TO SELF: ALL code blocks finish with ;
#==========================================================

######## Variables #######
my $myname = `whoami`;
$myname =~ s/(\n)$//;

####### Start of main script #######
print "Hello $myname, how are you doing today?\n";

Just google for perl and regex to find more on this or take a look at "learning pearl" published by O'Reilly.

what the "$myname =~...." does is this:

substitute the (\n) controll sequence at the very end (indicatd by $) of the initial string with "nothing".

Elukyz · 06-15-2007, 06:51 PM

Isn't it funny how you stumble upon answers right after you ask a question....

Ok, so I found a function built into perl, chmop() that can do it for me. (URL: http://perldoc.perl.org/functions/chomp.html) However, is it possible for me to use it for all variables once defined?

Elukyz · 06-15-2007, 06:54 PM

Quote:

Originally Posted by rtspitz

the output of $myname = `whoami`; contains the username + \n at the end !
that's why a new line is started.

you can get rid of it with a substitition based on "regular expressions" like this:

Code:

#!/usr/bin/perl -w

#==========================================================
# Last updated: June 11, 2007
# NOTE TO SELF: ALL code blocks finish with ;
#==========================================================

######## Variables #######
my $myname = `whoami`;
$myname =~ s/(\n)$//;

####### Start of main script #######
print "Hello $myname, how are you doing today?\n";

Just google for perl and regex to find more on this or take a look at "learning pearl" published by O'Reilly.

what the "$myname =~...." does is this:

substitute the (\n) controll sequence at the very end (indicatd by $) of the initial string with "nothing".

Thanks rtspitz, I was typing my post when you must've posted yours. I will look into that feature as well.

Sorry, wjevans_7d1@yahoo.co , I was probably looking and typing when you were posting your post as well. Thank you for your input all.

taylor_venable · 06-15-2007, 07:22 PM

Quote:

Originally Posted by Elukyz

However, is it possible for me to use it for all variables once defined?

As long as said variable is a scalar string, yes. Otherwise, you can call chomp() on it, but there won't be any effect. (In other words, chomping an array or hash does not change the object, chomping undef does nothing; the same goes for chomping a scalar number.)

wjevans_7d1@yahoo.co · 06-16-2007, 11:31 AM

Quote:

chomping an array or hash does not change the object

I beg to differ. I ran this Perl script:

Code:

#!/usr/bin/perl

@the_array=("line_one\n","line_two\n","line_three\n");

$the_hash{"aaa"}="xxx\n";
$the_hash{"bbb"}="yyy\n";
$the_hash{"ccc"}="zzz\n";

print("'@the_array'\n");

print("'",%the_hash,"'\n");

print("We are now going to chomp() both.\n");

chomp(@the_array);

chomp(%the_hash);

print("'@the_array'\n");

print("'",%the_hash,"'\n");

... and got this output:

Code:

'line_one
 line_two
 line_three
'
'bbbyyy
aaaxxx
ccczzz
'
We are now going to chomp() both.
'line_one line_two line_three'
'bbbyyyaaaxxxccczzz'

taylor_venable · 06-16-2007, 04:16 PM

You're absolutely right. I'm sorry, I don't know what I was thinking.

cramer · 06-16-2007, 05:59 PM

I would stick with the chomp() function instead of using regular expressions if all you want to remove is the new line character (/n).

chrism01 · 06-17-2007, 12:22 AM

Yeah, chomp() is safe and has Perl's DWIM (Do What I Mean) functionality that you'll find in a lot of Perl fns/operators.
Incidentally, chomping an array is handy if you want to process small files in mem, instead of reading from the disk & processing rec-by-rec. eg

open(FILE"<yourfile") or die "open failed: $!\n";
@file_recs = <FILE>;
close(FILE) or die "close failed: $!\n";
chomp(@file_recs);