On 21 Mar 2003 at 20:32, Matthew Stapleton wrote:
> Hello,
>
> I am learning Perl and having some fun with it. In a script I am writing
> I am wanting to read a line of a file and then extract a digit from the
> beginning of the line. A typical line looks something like this:
>
> 100. text text text
>
> So I am using a file handle to open the file and read the lines on by one
> with a while loop.
>
> while (<TXT>){}
>
> That part is pretty straight forward. Each line is then given to $_
>
> But how do I get just the digit at the beginning of the line out of $_ ?
> I thought about adding zero to $_ and then passing this to another
> variable but this does not seem to work.
>
> Can someone help me?
>
> Thanks,
>
>
> Matthew Stapleton
>
Welcome to Perl, Matthew.
You can (and in this case probably should)
use a regular expression; within your 'loop',
with your line in $_, try:
while (<TXT>){
chomp; # strips NL char at end of line
next unless $_; # skips if empty line
my ($nbr) = /^(\d)/;
next unless $nbr; # line did not begin w/digit
print "$nbr\n"; # show result
}
The meat of the above is the regex:
/^(\d)/;
Where:
/ is the regex delimiter
^ says match at start of variable, $_
( 'capture' until )
\d any digit 0-9
) end of 'capture'
/ end of regex
The (...) capture feature allows you to capture
matched parts of a regex; by default, the first
captured is put into special variable $1, the
second into $2, etc; if you call the regex in
list context (assigning the result to a list
or array), the captures are put into that list/
array. That's why I wrote ($nbr) above - list
context.
Now, if the first character of the line is not
a digit 0-9, nothing will be captured and $nbr
will be undefined.
Otherwise, $nbr contains the first digit of the
line.
If you would rather capture the entire number
that starts the line, use:
my ($nbr) = /^(\d+)/;
\d+ says one or more (+) digits.
Study your regexs! :)
Aloha => Beau;
PS: untested - you have to find my typos...
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