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How can I use a variable as a variable name in Perl?
(3 answers)
Closed 8 years ago.
I have an array of strings that I want to use in a loop and then call later as names of a hash. I wrote a test file to play around with it, but I can't get it to work no matter how hard I am trying. It keeps giving me "can't use string as a hash ref while strict refs is in use". I can turn off strict refs, but then the code simply skips those lines and doesn't do what I want. Is there any way to evaluate a variable that contains a string and then pipe it to the name of a hash?
Example code:
#usr/bin/perl
use strict;
my %combined = ();
my %highmut = ();
$combined{'a'} = 1;
$combined{'b'} = 2;
$highmut{'c'} = 3;
$highmut{'d'} = 4;
my #counts = ('combined', 'highmut');
foreach my $count (#counts) {
my $file = $count . '.txt';
open(my $random, ">>", $file);
foreach my $key (keys %{$count}) {
print $random "key: $key \t %{$count{$key}} \n";
close($random);
}
}
Specifically, the issues are with %{$count} and %{$count{$key}} in the last few lines.
What I want is to evaluate $count (as say combined) and then feed it to use as hash name (%combined).
Is there any way to do this?
Thanks
You can, but it's a bad idea. Consider using a multidimensional data structure instead.
my %data = ( combined => { a => 1,
b => 2,
},
highmut => { c => 3,
d => 4,
},
);
foreach my $count (keys %data) {
my $file = $count . '.txt';
open(my $random, ">>", $file);
foreach my $key (keys %{$data{$count}}) {
print $random "key: $key \t $data{$count}{$key} \n";
}
close($random);
}
Note: you also had a bug in your program flow. You open a file based on the count type, loop over your keys, write the first one, close the file, and continue looping with no filehandle open to write to for subsequent keys. I therefore moved your close out of the iteration over keys.
Further reading:
http://perldoc.perl.org/perlfaq7.html#How-can-I-use-a-variable-as-a-variable-name%3f
perl variable substitution in variable name
In Perl, how can I use a string as a variable name?
Using variable strings to access named hashes is a bad idea for all kinds of maintainability and spooky-action-at-a-distance reasons. That's why use strict 'refs' doesn't let you do it on purpose or by accident. If that's what you really want to do, disable strict refs:
foreach my $count (#counts) {
my $file = $count . '.txt';
open(my $random, ">>", $file);
no strict 'refs';
foreach my $key (keys %{$count}) {
...
Related
So, well I am trying around again and now I am stuck.
while (<KOERGEBNIS>){
my $counter = 0;
my $curline = $_;
for (my $run = 0; $run < $arrayvalue; $run++){
if ($curline =~ m/#tidgef[$counter]/){
my $row = substr($curline, 0, 140);
push #array$counter, $row;
print "Row $. was saved in ID: #filtered[$counter]\n";
}
$counter++;
}
}
Background is that I want to save all lines beginning with the same 8 characters in the same array so I can count the lines and start working with those arrays. The only thing I could think of right now is with switch and cases but I thought I'd ask first before throwing this code to garbage.
Example:
if theres a line in a .txt like this:
50004000_xxxxxxxxxxxxxx31
50004000_xxxxxxxxxxxxxx33
60004001_xxxxxxxxxxxxxx11
60004001_xxxxxxxxxxxxxx45
I took the first 8 chars of each line and used uniq to filter duplicates and saved them in the array #tidgef, now I want to save Line1 and Line2 in #array1 or even better #array50004000 and Line4 and Line4 to #array2 or #array60004001.
I hope I explained my problem well enough! thank you guys
You're hovering dangerously close to an idea called "symbolic references" (also known as "use a variable to get a variable's name"). It's a very bad idea, for all sorts of reasons.
It's a much better idea to use this as an excuse to learn about complex data structures in Perl. It's not really clear what you want to do with this data, but this example should get you started:
#!/usr/bin/perl
use strict;
use warnings;
use 5.010;
use Data::Dumper;
my %lines;
while (<DATA>) {
chomp;
my $key = substr($_, 0, 8);
push #{$lines{$key}}, $_;
}
say Dumper \%lines;
__DATA__
50004000_xxxxxxxxxxxxxx31
50004000_xxxxxxxxxxxxxx33
60004001_xxxxxxxxxxxxxx11
60004001_xxxxxxxxxxxxxx45
You should think carefully about why you want arrays called #array50004000 #array60004001. Your program could create them, but you have no way of knowing what those names are. While the code is running, unless you are stepping through it with the debugger, they may be called #x and #y for all you know. You can't even dump their contents because you have no idea what to dump
What you're looking for is a hash, specifically a hash of arrays. Unlike the symbol table, there are operators like keys, values and each that will allow you to enquire what values have been stored in a hash
Your code would look something like this. I have used the example data from your question and put it into myfile
use strict;
use warnings 'all';
my %data;
open KOERGEBNIS, '<', 'myfile' or die $!;
while ( <KOERGEBNIS> ) {
chomp;
my ($key) = split /_/;
push #{ $data{$key} }, $_;
}
for my $key ( sort keys %data ) {
my $val = $data{$key};
print $key, "\n";
print " $_\n" for #$val;
print "\n";
}
output
50004000
50004000_xxxxxxxxxxxxxx31
50004000_xxxxxxxxxxxxxx33
60004001
60004001_xxxxxxxxxxxxxx11
60004001_xxxxxxxxxxxxxx45
I'm not sure how to correctly initialize my hash - I'm trying to create a key/value pair for values in coupled lines in my input file.
For example, my input looks like this:
#cluster t.18
46421 ../../../output###.txt/
#cluster t.34
41554 ../../../output###.txt/
I'm extracting the t number from line 1 (#cluster line) and matching it to output###.txt in the second line (line starting with 46421). However, I can't seem to get these values into my hash with the script that I have written.
#!/usr/bin/perl
use warnings;
use strict;
my $key;
my $value;
my %hash;
my $filename = 'input.txt';
open my $fh, '<', $filename or die "Can't open $filename: $!";
while (my $line = <$fh>) {
chomp $line;
if ($line =~ m/^\#cluster/) {
my #fields = split /(\d+)/, $line;
my $key = $fields[1];
}
elsif ($line =~ m/^(\d+)/) {
my #output = split /\//, $line;
my $value = $output[5];
}
$hash{$key} = $value;
}
It's a good idea, but your $key that is created with my in the if block is a local variable scoped to that block, masking the global $key. Inside the if block the symbol $key has nothing to do with the one you nicely declared upfront. See my in perlsub.
This local $key goes out of scope as soon as if is done and does not exist outside the if block. The global $key is again available after the if, being visible elsewhere in the loop, but is undefined since it has never been assigned to. The same goes for $value in the elsif block.
Just drop the my declaration inside the loop, thus assign to those global variables (as intended?). So, $key = ... and $value = ..., and the hash will be assigned correctly.
Note -- this is about how to get that hash assignment right. I don't know how your actual data looks and whether the line is parsed correctly. Here is a toy input.txt
#cluster t.1
1111 ../../../output1.1.txt/
#cluster t.2
2222 ../../../output2.2.txt/
I pick the 4th field instead of the 6th, $value = $output[3];, and add
print "$_ => $hash{$_}\n" for keys %hash;
after the loop. This prints
1 => output1.1.txt
2 => output2.2.txt
I am not sure whether this is what you want but the hash is built fine.
A comment on choice of tools in parsing
You parse the lines for numbers, by using the property of split to return the separators as well, when they are captured. That is neat, but in some sense it reverses its main purpose, which is to extract other components from the string, as delimited by the pattern. Thus it may make the purpose of the code a little bit convoluted, and you also have to index very precisely to retrieve what you need.
Instead of using split to extract the delimiter itself, which is given by a regex, why not extract it by a regex? That makes the intention crystal clear, too. For example, with input
#cluster t.10 has 4319 elements, 0 subclusters
37652 ../../../../clust/output43888.txt 1.397428
the parsing can go as
if ($line =~ m/^\#cluster/) {
($key) = $line =~ /t\.(\d+)/;
}
elsif ($line =~ m/^(\d+)/) {
($value) = $line =~ m|.*/(\w+\.txt)|;
}
$hash{$key} = $value if defined $key and defined $value;
where t\. and \.txt are added to more precisely specify the targets. If the target strings aren't certain to have that precise form, just capture \d+, and in the second case all non-space after the last /, say by m|^\d+.*/(\S+)|. We use the greediness of .*, which matches everything possible up to the thing that comes after it (a /), thus all the way to the very last /.
Then you can also reduce it to a single regex for each line, for example
if ($line =~ m/^\#cluster\s+t\.(\d+)/) {
$key = $1;
}
elsif ($line =~ m|^\d+.*/(\w+\.txt)|) {
$value = $1;
}
Note that I've added a condition to the hash assignment. The original code in fact assigns an undef on the first iteration, since no $value had yet been seen at that point. This is overwritten on the next iteration and we don't see it if we only print the hash afterwards. The condition also guards you against failed matches, for malformatted lines or such. Of course, far better checks can be run.
I am looking for code in Perl similar to
my #lines1 = split /\n/, $str1;
my #lines2 = split /\n/, $str2;
for (int $i=0; $i<lines1.length; $i++)
{
if (lines1[$i] ~= lines2[$i])
print "difference in line $i \n";
}
To compare two strings line by line and show the lines at which there is any difference.
I know what I have written is mixture of C/Perl/Pseudo-code. How do I write it in the way that it works on Perl?
What you have written is sort of ok, except you cannot use that notation in Perl lines1.length, int $i, and ~= is not an operator, you mean =~, but that is the wrong tool here. Also if must have a block { } after it.
What you want is simply $i < #lines1 to get the array size, my $i to declare a lexical variable, and eq for string comparison. Along with if ( ... ) { ... }.
Technically you can use the binding operator to perform a string comparison, for example:
"foo" =~ "foobar"
But it is not a good idea when comparing literal strings, because you can get partial matches, and you need to escape meta characters. Therefore it is easier to just use eq.
Using C-style for loops is valid, but the more Perl-ish way is to use this notation:
for my $i (0 .. $#lines1)
Which will iterate over the range 0 to the max index of the array.
Perl allows you to open filehandles on strings by using a reference to the scalar variable that holds the string:
open my $string1_fh, '<', \$string1 or die '...';
open my $string2_fh, '<', \$string2 or die '...';
while( my $line1 = <$string1_fh> ) {
my $line2 = <$string2_fh>;
....
}
But, depending on what you mean by difference (does that include insertion or deletion of lines?), you might want something different.
There are several modules on CPAN that you can inspect for ideas, such as Test::LongString or Algorithm::Diff.
my #lines1 = split(/^/, $str1);
my #lines2 = split(/^/, $str2);
# splits at start of line
# use /\n/ if you want to ignore newline and trailing spaces
for ($i=0; $i < #lines1; $i++) {
print "difference in line $i \n" if (lines1[$i] ne lines2[$i]);
}
Comparing Arrays is a way easier if you create a Hashmap out of it...
#Searching the difference
#isect = ();
#diff = ();
%count = ();
foreach $item ( #array1, #array2 ) { $count{$item}++; }
foreach $item ( keys %count ) {
if ( $count{$item} == 2 ) {
push #isect, $item;
}
else {
push #diff, $item;
}
}
#Output
print "Different= #diff\n\n";
print "\nA Array = #array1\n";
print "\nB Array = #array2\n";
print "\nIntersect Array = #isect\n";
Even after spliting you could compare them as Array.
I am having an undesired interaction with a foreach loop and a while that I don't quite understand. I have a normal for loop, and then a foreach loop going through an array. I create a string (representing a file name) with both and then open the file and read it.
The code I use is here:
#array=(1,2);
for($y=0;$y<2;$y++)
{
foreach(#array)
{
print "#array\n";
$name="/Users/jorge/$_\_vs_$y\.txt";
print "$name\n";
open(INFILE,"$name") or die "Can't open files!\n";
while(<INFILE>)
{
$line=$_;
}
}
}
and the output is:
array: 1 2
/Users/jorge/1_vs_0.txt
array: 2
/Users/jorge/2_vs_0.txt
array:
/Users/jorge/_vs_1.txt
Seems that somehow the while loop is shortening my array, if I remove the:
while(<INFILE>)
it works as intented, also if I change the foreach too:
foreach $tmp (#array)
and use $tmp instead of $_, it also works as intended, the output looks like this:
array: 1 2
/Users/jorge/1_vs_0.txt
array: 1 2
/Users/jorge/2_vs_0.txt
array: 1 2
/Users/jorge/1_vs_1.txt
array: 1 2
/Users/jorge/2_vs_1.txt
array: 1 2
/Users/jorge/1_vs_2.txt
You're using $_ as the loop control variable on two nested loops. Instead, you should give each loop its own variable.
Not only is the inner loop changing the value of the control variable for the outer loop, but it's also changing the actual array being looped over. That's because the loop control variable in Perl's for/foreach aliases the elements of the array, so when the <INFILE> construct reads a line into $_, it overwrites the current element of #array with that line. When the while loop finishes reading the file, $_ comes out of the last <INFILE> as undefined, which means the most-recently processed element of #array will always be undefined when you get back to the top of the foreach loop.
You should also be declaring your variables with my, using a lexical scalar instead of a bareword as a file handle, and using the the three-argument version of open, so I've made those changes below as well. But the solution to your shrinking-array problem is just the use of an explicit variable instead of the default $_ for at least one of the two loops.
my #array = (1, 2);
for (my $y = 0; $y < 2; $y++)
{
foreach my $x (#array) # using $x instead of $_
{
print "#array\n";
my $name = "/Users/jorge/${x}_vs_$y.txt";
print "$name\n";
open my $infile, '<', $name or die "$0: can't open file '$name': $!\n";
while (my $line = <$infile>) # using $line instead of $_
{
# do something with $line here
}
}
}
Your while loop overwrites content of array as it uses $_ which is aliased to #array elements.
It is best to use lexical (my) variable when reading file using while,
while (my $line = <INFILE>) {
# ..
}
I have a file that looks like this:
[options42BuySide]
logged-check-times=06:01:00
logged-check-address=192.168.3.4
logged-check-reply=192.168.2.5
logged-check-vac-days=sat,sun
start-time=06:01:00
stop-time=19:00:00
falldown=logwrite after 10000
failtolog=logwrite after 10000
listento=all
global-search-text=Target Down. This message is stored;
[stock42BuySide]
logged-check-times=06:01:00
logged-check-address=192.168.2.13
logged-check-reply=192.168.2.54
logged-check-vac-days=sat,sun
start-time=06:01:00
stop-time=18:00:00
The script grinds the list down to just the name, start and stop time.
sellSide40, start-time=07:05:00, stop-time=17:59:00
SellSide42, start-time=07:06:00, stop-time=17:29:00
SellSide44, start-time=07:31:00, stop-time=16:55:00
42SellSide, start-time=09:01:00, stop-time=16:59:00
The problem is that I would like to filter out specific names from the file with comand line parameters.
I am trying to use the #ARGV array and grep the command line values out of the #nametimes array. Something like :
capser#capser$ ./get_start_stop SorosSellSide42 ETFBuySide42
The script works fine for parsing the file - I just need help on the command line array
#!/usr/bin/perl
use strict ;
use warnings ;
my ($name , $start, $stop, $specific);
my #nametimes;
my $inifile = "/var/log/Alert.ini";
open ( my $FILE, '<', "$inifile") or die ("could not open the file -- $!");
while(<$FILE>) {
chomp ;
if (/\[(\w+)\]/) {
$name = $1;
} elsif (/(start-time=\d+:\d+:\d+)/) {
$start = $1;
} elsif (/(stop-time=\d+:\d+:\d+)/) {
$stop = $1;
push (#nametimes, "$name, $start, $stop");
}
}
for ($a = 0; $a >= $#ARGV ; $a++) {
$specific = (grep /$ARGV[$a]/, #nametimes) ;
print "$specific\n";
}
It is probably pretty easy - however I have worked on it for days, and I am the only guy that uses perl in this shop. I don't have anyone to ask and the googlize is not panning out. I apologize in advance for angering the perl deities who are sure to yell at me for asking such and easy question.
Your construct for looping over #ARGV is a bit unwieldy - the more common way of doing that would be:
for my $name (#ARGV) {
#do something
}
But really, you don't even need to loop over it. You can just join them all directly into a single regular expression:
my $names = join("|", #ARGV);
my #matches = grep { /\b($names)\b/ } #nametimes;
I've used \b in the regex here - that indicates a word boundary, so the argument SellSide4 wouldn't match SellSide42. That may or may not be what you want...
Use an array to store the results from the grep(), not a scalar. Push them, not assign. Otherwise the second iteration of the for loop will overwrite results. Something like:
for my $el ( #ARGV ) {
push #specific, grep { /$el/ } #nametimes);
};
print join "\n", #specific;
The easiest thing to do is to store your INI file as a structure. Then, you can go through your structure and pull out what you want. The simplest structure would be a hash of hashes. Where your heading is the key to the outer hash, and the inner hash is keyed by the parameter:
Here's is creating the basic structure:
use warnings;
use strict;
use autodie;
use feature qw(say);
use Data::Dumper;
use constant INI_FILE => "test.file.txt";
open my $ini_fh, "<", INI_FILE;
my %ini_file;
my $heading;
while ( my $line = <$ini_fh> ) {
chomp $line;
if ( $line =~ /\[(.*)\]/ ) { #Headhing name
$heading = $1;
}
elsif ( $line =~ /(.+?)\s*=\s*(.+)/ ) {
my $parameter = $1;
my $value = $2;
$ini_file{$heading}->{$parameter} = $value;
}
else {
say "Invalid line $. - $line";
}
}
After this, the structure will look like this:
$VAR1 = {
'options42BuySide' => {
'stop-time' => '19:00:00',
'listento' => 'all',
'logged-check-reply' => '192.168.2.5',
'logged-check-vac-days' => 'sat,sun',
'falldown' => 'logwrite after 10000',
'start-time' => '06:01:00',
'logged-check-address' => '192.168.3.4',
'logged-check-times' => '06:01:00',
'failtolog' => 'logwrite after 10000',
'global-search-text' => 'Target Down. This message is stored;'
},
'stock42BuySide' => {
'stop-time' => '18:00:00',
'start-time' => '06:01:00',
'logged-check-reply' => '192.168.2.54',
'logged-check-address' => '192.168.2.13',
'logged-check-vac-days' => 'sat,sun',
'logged-check-times' => '06:01:00'
}
};
Now, all you have to do is parse your structure and pull the information you want out of it:
for my $heading ( sort keys %ini_file ) {
say "$heading " . $ini_file{$heading}->{"start-time"} . " " . $ini_file{$heading}->{"stop-time"};
}
You could easily modify this last loop to skip the headings you want, or to print out the exact parameters you want.
I would also recommend using Getopt::Long to parse your command line parameters:
my_file -include SorosSellSide42 -include ETFBuySide42 -param start-time -param stop-time
Getopt::Long could store your parameters in arrays. For example. It would put all the -include parameters in an #includes array and all the -param parameters in an #parameters array:
for my $heading ( #includes ) {
print "$heading ";
for my $parameter ( #parameters ) {
print "$ini_file{$heading}->{$parameter} . " ";
}
print "\n;
}
Of course, there needs to be lots of error checking (does the heading exist? What about the requested parameters?). But, this is the basic structure. Unless your file is extremely long, this is probably the easiest way to process it. If your file is extremely long, you could use the #includes and #parameters in the first loop as you read in the parameters and headings.