Perl regex - print only modified line (like sed -n 's///p')-CodePudding

I have a command that outputs text in the following format:

misc1=poiuyt
var1=qwerty
var2=asdfgh
var3=zxcvbn
misc2=lkjhgf

etc. I need to get the values for var1, var2, and var3 into variables in a perl script.

If I were writing a shell script, I'd do this:

OUTPUT=$(command | grep '^var-')
VAR1=$(echo "${OUTPUT}" | sed -ne 's/^var1=\(.*\)$/\1/p')
VAR2=$(echo "${OUTPUT}" | sed -ne 's/^var2=\(.*\)$/\1/p')
VAR3=$(echo "${OUTPUT}" | sed -ne 's/^var3=\(.*\)$/\1/p')

That populates OUTPUT with the basic content that I want (so I don't have to run the original command multiple times), and then I can pull out each value using sed VAR1 = 'qwerty', etc.

I've worked with perl in the past, but I'm pretty rusty. Here's the best I've been able to come up with:

my $output = `command | grep '^var'`;
(my $var1 = $output) =~ s/\bvar1=(.*)\b/$1/m;
print $var1

This correctly matches and references the value for var1, but it also returns the unmatched lines, so $var1 equals this:

qwerty
var2=asdfgh
var3=zxcvbn

With sed I'm able to tell it to print only the modified lines. Is there a way to do something similar with in perl? I can't find the equivalent of sed's p modifier in perl.

Conversely, is there a better way to extract those substrings from each line? I'm sure I could match match each line and split the contents or something like that, but was trying to stick with regex since that's how I'd typically solve this outside of perl.

Appreciate any guidance. I'm sure I'm missing something relatively simple.

CodePudding user response：

One way

my @values = map { /\bvar(?:1|2|3)\s*=\s*(.*)/ ? $1 : () } qx(command);

The qx operator ("backticks") returns a list of all lines of output when used in list context, here imposed by map. (In a scalar context it returns all output in a string, possibly multiline.) Then map extracts wanted values: the ternary operator in it returns the capture, or an empty list when there is no match (so filtering out such lines). Please adjust the regex as suitable.

Or one can break this up, taking all output, then filtering needed lines, then parsing them. That allows for more nuanced, staged processing. And then there are libraries for managing external commands that make more involved work much nicer.

CodePudding user response：

In scalar context, s/// and s///g return whether it found a match or not. So you can use

print $s if $s =~ s///;