Extract a number from a string.

[Adam]

Hi All,

Apologies if this is laughably simple, but it's been a long time since
I've used Perl, and I seem to suffer from Homer Simpson's problem:
every time I learn something new, it pushes old stuff out.

I'm trying to extract a number from a line of text returned by a
license-checking command. I open a pipe to the command, and read
through each line that is returned. When I find the text "Maximum..."
or "Current..." I want to extract and store the number in that line. I
tried using something like this to start with:

$lic_usage{$lic_type}{$max} = /\d+/ if (/Maximum/);
$lic_usage{$lic_type}{$cur} = /\d+/ if (/Current/);

Of course, this only stores a 1 ('True') when it finds the string, and
I want it to record the actual digits.

Help!

Cheers - Adam...

 

[Peter Wyzl]

Hi All,

Apologies if this is laughably simple, but it's been a long time since
I've used Perl, and I seem to suffer from Homer Simpson's problem:
every time I learn something new, it pushes old stuff out.

I'm trying to extract a number from a line of text returned by a
license-checking command. I open a pipe to the command, and read
through each line that is returned. When I find the text "Maximum..."
or "Current..." I want to extract and store the number in that line. I
tried using something like this to start with:

$lic_usage{$lic_type}{$max} = /\d+/ if (/Maximum/);
$lic_usage{$lic_type}{$cur} = /\d+/ if (/Current/);

You need to capture the numbers IF there is a match...

if (/Maximum/){$lic_usage{$lic_type}{$max} = $1 if (/(\d+)/)};

Because there are two conditionals involved (you don't want to assign from
$1 et al unless there was a match) I would write it like the above, or
perhaps less ambiguously like:

if (/Maximum/){
$lic_usage{$lic_type}{$max} = $1 if (/(\d+)/);
}

Check in perlre for info on the capturing parens.

 

[Anno Siegel]

Hi All,

Apologies if this is laughably simple, but it's been a long time since
I've used Perl, and I seem to suffer from Homer Simpson's problem:
every time I learn something new, it pushes old stuff out.

I'm trying to extract a number from a line of text returned by a
license-checking command. I open a pipe to the command, and read
through each line that is returned. When I find the text "Maximum..."
or "Current..." I want to extract and store the number in that line. I
tried using something like this to start with:

$lic_usage{$lic_type}{$max} = /\d+/ if (/Maximum/);
$lic_usage{$lic_type}{$cur} = /\d+/ if (/Current/);

Of course, this only stores a 1 ('True') when it finds the string, and
I want it to record the actual digits.

Too few parentheses in some places, more than needed in others.

( $lic_usage{ $lic_type}{ $max}) = /(\d+)/ if /Maximum/;

The parentheses around the left side of "=" put the right side
in array context. That makes the regex return the list of captured
matches. The parentheses around "\d+" in the regex capture the
digits. The condition of a statement-modifying "if" doesn't need
parentheses.

Of course, the value of $lic_usage{ $lic_type}{ $max} must be checked
before use, there is no guarantee that the statement ever assigns
anything.

Anno

 

[Adam]

You need to capture the numbers IF there is a match...

if (/Maximum/){$lic_usage{$lic_type}{$max} = $1 if (/(\d+)/)};

Because there are two conditionals involved (you don't want to assign from
$1 et al unless there was a match) I would write it like the above, or
perhaps less ambiguously like:

if (/Maximum/){
$lic_usage{$lic_type}{$max} = $1 if (/(\d+)/);
}

Check in perlre for info on the capturing parens.

Thank you Peter (and anyone else who answers before Google gets this
reply out)...

It was indeed because I had omitted the parentheses around '\d+' -
although I discovered it *is* possible to present it as a single line
by assigning the lic_usage hash in list context, thus:

($lic_usage{$lic_type}{$max}) = /(\d+)/ if (/Maximum/);

I was so nearly there!

Thanks again - Adam...

 

[John W. Krahn]

Apologies if this is laughably simple, but it's been a long time since
I've used Perl, and I seem to suffer from Homer Simpson's problem:
every time I learn something new, it pushes old stuff out.

I'm trying to extract a number from a line of text returned by a
license-checking command. I open a pipe to the command, and read
through each line that is returned. When I find the text "Maximum..."
or "Current..." I want to extract and store the number in that line. I
tried using something like this to start with:

$lic_usage{$lic_type}{$max} = /\d+/ if (/Maximum/);
$lic_usage{$lic_type}{$cur} = /\d+/ if (/Current/);

Of course, this only stores a 1 ('True') when it finds the string, and
I want it to record the actual digits.

$lic_usage{$lic_type}{$max} = $1 if /Maximum/ && /(\d+)/;
$lic_usage{$lic_type}{$cur} = $1 if /Current/ && /(\d+)/;



John

 

[David Filmer]

Out of curiosity, are you trying to parse the output from IBM's LUM
(i4lls/i4blt) license manager?

 

[Peter Wyzl]

news:<[email protected]>...

($lic_usage{$lic_type}{$max}) = /(\d+)/ if (/Maximum/);

What happens here when /Maximum/ matches and /(\d+)/ fails to capture
anything?

You end up assigning whatever happens to be in $1 at that time (maybe
nothing, more likely the result of the last successful match) to
$lic_usage{$lic_type}{$max}. This is a _bad_ thing.

That is precisely why I showed it as two separate matches. See John Krahn's
post for a nice way to do both conditionals in a single line without that
risk.

 

[Ben Morrow]

What happens here when /Maximum/ matches and /(\d+)/ fails to capture
anything?

You end up assigning whatever happens to be in $1 at that time (maybe
nothing, more likely the result of the last successful match) to
$lic_usage{$lic_type}{$max}. This is a _bad_ thing.

Did you try it? You actually get the empty string.

You should never use the $n variables without checking the match
succeeded, but list assognment of a match does not use the $n variables.

Ben

 

[Brian McCauley]

Did you try it? You actually get the empty string.

Did you try it? You actually get the undefined value.

 

[Peter Wyzl]

Did you try it? You actually get the empty string.

You should never use the $n variables without checking the match
succeeded, but list assognment of a match does not use the $n variables.

No, I didn't try it cos I was making the point that it was 'a bad thing'(tm)
and not what I had replied with earlier.

 

[Ben Morrow]

Did you try it? You actually get the undefined value.

I did, actually, but I missed the brackets around $y in

my ($y) = /(\d+)/ if /Maximum/;

so I got the empty string instead... whoops.

Ben