How can I get the name of the input file in a Perl one-liner?

File monday.csv

223.22;1256.4
227.08;1244.8
228.08;1244.7
229.13;1255.0
227.89;1243.2
224.77;1277.8

File tuesday.csv

227.02;1266.3
227.09;1234.9
225.18;开发者_StackOverflow1244.7
224.13;1255.3
228.59;1263.2
224.70;1247.6

This Perl one-liner gives me the row with the highest value in the second column from the rows where in the first column the first three digits are 227 or 226 from the file "monday.csv":

perl -F\; -ane '$hash{$_} = $F[1] if /22[78]/; END{ print and exit for sort{ $hash{$b} <=> $hash{$a} } keys %hash }' monday.csv

This Perl one-liner gives me the row with the highest value in the second column from the rows where in the first column the first 3 digits are 227 or 226 from all *day.csv files:

perl -F\; -ane '$hash{$_} = $F[1] if /22[78]/; END{ print and exit for sort{ $hash{$b} <=> $hash{$a} } keys %hash }' *day.csv

How could I rewrite this one-liner to get an output like

filename : "row with the highest value in the second column from the rows where in the first column the first 3 digits are 227 or 226 from the file 'filename.csv'"

for each *day.csv file?

You can use $ARGV for the current file name. If you're only interested in the max, no need to store all the values and then sort them; instead, just store the max for each file. Also, your regex probably should be anchored to the start of the line.

# Line breaks added for display purposes.
perl -F\; -ane '
    $max{$ARGV} = $F[1] if /^22[78]/ and $F[1] > $max{$ARGV};
    END{ print "$_\t$max{$_}" for sort keys %max}
' *day.csv

Or, if you want to store the entire line where the max occurs:

perl -F\; -ane '
    ($max{$ARGV}{ln}, $max{$ARGV}{mx}) = ($_, $F[1])
        if /^22[78]/ and $F[1] > $max{$ARGV}{mx};
    END{ print "$_\t$max{$_}{ln}" for sort keys %max}
' *day.csv

The filename is contained in the $ARGV variable:

$ARGV

contains the name of the current file when reading from <>.

However, the one-liners presented have an issue; what if you have repeated values of your first column?

A better one-liner would be:

$ perl -F/;/ -MList::Util=max -lane 'push @{ $wanted{$ARGV} }, $F[1] if $F[0] =~ /22[78]/; } END { print "$ARGV : ", max(@{ $wanted{$_} }) for keys %wanted;' *.csv

Based on the comment:

$ perl -F/;/ -lane '$wanted{$ARGV} = \@F if $F[1] >= $wanted->{$ARGV}[1] && $F[0] =~ /22[78]/; } END { print "$_ : @$wanted{$_}" for keys %wanted;' *.csv

It seems that you can use $ARGV.