formatting line numbers 1

[jjohnn]

My task (from a perl tutorial

http://www.comp.leeds.ac.uk/Perl/control.html)

is to alter a program that prints line numbers on a file so that ->
"line numbers are printed as 001, 002, ..., 009, 010, 011, 012, etc. To do this you should only need to change one line by inserting an extra four characters. Perl's clever like that."
I print the line numbers easily enough:

$file = 'sta.txt';
open (TEXT, $file);
my $linenum;

while ($line = <TEXT>){
$linenum++;
print &quot;$linenum &quot;.&quot;$line&quot;;
}
The four characters to add to this script to format the line numbers mystifies me. Any suggestions?

 

[justice41]

Initialize $linenum as

my $linenum = "000";

jaa

 

[rosenk]

[tt]printf &quot;%03d %s&quot;, $linenum, $line;[/tt]

 

[jjohnn]

Thanks again.

 

[jjohnn]

But wait; why does the &quot;000&quot; approach *not* work with the diamond operator, reading the filename off the command line?

Using <> doesn't give me the leading zeros, but the same code with the named filehandle does give me the leading zeroes.

 

[icrf]

<> is equivilent to <STDIN>, or what's generally the keyboard.

Unless that wasn't the question at all. What about reading a filename off the command line? For simple command line arguments, you can use the @ARGV array. ----------------------------------------------------------------------------------
...but I'm just a C man trying to see the light

 

[jjohnn]

$file = 'sta.txt';
open (TEXT, $file);
my $linenum =&quot;000&quot;;

while ($line = <TEXT>){
$linenum++;
print &quot;$linenum &quot;.&quot;$line&quot;;
}

This script formats the line numbers for the named file like 001,002...0067,0068. However, the exact same script, with the file name invoked on the command line instead:

perl linenum.pl stat.text [entered on command line]

my $linenum;

while ($line = <>){
$linenum++;
print &quot;$linenum &quot;.&quot;$line&quot;;
}
gives linenumbers as 1,2...67,68.
Why the difference with the same code?

 

[jjohnn]

&quot;linenum&quot; in that example is both the name of a variable in the script and the name of the perl script itself. Bad naming for this example.

 

[rosenk]

The second example is missing the crucial [tt]my $linenum = &quot;000&quot;;[/tt] as Justice suggested earlier. (I personally didn't know that perl would increment that way.)

[tt]my $linenum = &quot;000&quot;;
foreach (0..2) {
$linenum++;
print &quot;$linenum\n&quot;;
}[/tt]

gives:
[tt]001
002
003[/tt]

While:
[tt]my $linenum;
foreach (0..2) {
$linenum++;
print &quot;$linenum\n&quot;;
}[/tt]

gives:
[tt]1
2
3[/tt]