Blowing some white space into your command shows that there is a pattern that we might take advantage of.

plot $years $yscala 

"$abc_this_01" title "" with errorbars lt rgb "$color_abc" lw 2,
"$abc_this_01" title "{/Helvetica=10 ABC_Stuff}" with lines lt rgb "$c
+olor_abc" lw 3,

"$def_this_01" title "" with errorbars lt rgb "$color_def" lw 2,
"$def_this_01" title "{/Helvetica=10 DEF_Stuff}" with lines lt rgb "$c
+olor_def" lw 3,

"$ghi_this_01" title "" with errorbars lt rgb "$color_ghi" lw 2,
"$ghi_this_01" title "{/Helvetica=10 GHI_Stuff}" with lines lt rgb "$c
+olor_ghi" lw 3,

"$jkl_this_01" title "" with errorbars lt rgb "$color_jkl" lw 2,
"$jkl_this_01" title "{/Helvetica=10 JKL_Stuff}" with lines lt rgb "$c
+olor_jkl" lw 5,

"$mno_this_01" with steps lt 1 lw 5 title "{/Helvetica=10 Abnormality 
+Border}"
[download]

We could consider putting the data into a hash and then feed that into a template. I've used sprintf here but there are many alternatives. I've made some guesses about the actual spec.

#! /usr/perl/bin

use warnings;
use strict;

my %args = (
  years => 2011,
  yscala => q{xxx},
  sources => [
    {
      source => q{abc},
      color => q{red},
    },
    {
      source => q{def},
      color => q{blue},
    },
    {
      source => q{ghi},
      color => q{yellow},
    },
    {
      source => q{jkl},
      color => q{green},
    },
  ],
  topic => q{this},
  number => q{01},
  abnormality_border => q{mno},
);

my $cmd = build_command(%args);
print $cmd;

sub build_command {

  my %args = @_;
  
  my $cmd = sprintf(
    qq{plot %s %s\n\n}, 
    $args{years}, 
    $args{yscala}
  );
  
  for my $source (@{$args{sources}}){
  
    $cmd .= sprintf(
      qq{"C:/Stuff/%s_%s_%s.csv" title "" with errorbars lt rgb "%s_%s
+" lw 2,\n}, 
      $source->{source}, 
      $args{topic}, 
      $args{number}, 
      $source->{color},
      $source->{source},
    );

    $cmd .= sprintf(
      qq{"C:/Stuff/%s_%s_%s.csv" title "{/Helvetica=10 ABC_Stuff}" wit
+h lines lt rgb "%s_%s" lw 3,\n\n},
      $source->{source},
      $args{topic},
      $args{number},
      $source->{color},
      $source->{source},
    );
  }
  
  $cmd .= sprintf(
    qq{"C:/Stuff/%s_%s_%s.csv" with steps lt 1 lw 5 title "{/Helvetica
+=10 Abnormality Border}"},
    $args{abnormality_border},
    $args{topic},
    $args{number},
  );
  
  return $cmd;

}
[download]

output

plot 2011 xxx

"C:/Stuff/abc_this_01.csv" title "" with errorbars lt rgb "red_abc" lw
+ 2,
"C:/Stuff/abc_this_01.csv" title "{/Helvetica=10 ABC_Stuff}" with line
+s lt rgb "red_abc" lw 3,

"C:/Stuff/def_this_01.csv" title "" with errorbars lt rgb "blue_def" l
+w 2,
"C:/Stuff/def_this_01.csv" title "{/Helvetica=10 ABC_Stuff}" with line
+s lt rgb "blue_def" lw 3,

"C:/Stuff/ghi_this_01.csv" title "" with errorbars lt rgb "yellow_ghi"
+ lw 2,
"C:/Stuff/ghi_this_01.csv" title "{/Helvetica=10 ABC_Stuff}" with line
+s lt rgb "yellow_ghi" lw 3,

"C:/Stuff/jkl_this_01.csv" title "" with errorbars lt rgb "green_jkl" 
+lw 2,
"C:/Stuff/jkl_this_01.csv" title "{/Helvetica=10 ABC_Stuff}" with line
+s lt rgb "green_jkl" lw 3,

"C:/Stuff/mno_this_01.csv" with steps lt 1 lw 5 title "{/Helvetica=10 
+Abnormality Border}"
[download]

The initial hash (the data) could be kept in a separate file and read in by the script. I often find keeping the data and code separate can ease updating/maintainance. Taking it a bit further keeping the actual templates in a separate file wouldn't hurt either.

When you have it working nicely you would obviously take the white space out.

updated: added output and included the csv file.

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