1  ##
     2  perl -lne 'chomp;                               # remove the newline at the end of the current line being processed
     3             if ($ARGV eq "img.txt") {            # if the current line is of file "img.txt" then
     4               if (/.*(\d{3}[_-]\d\d[ab]).*/i) {  # extract the "NNN[_-]NN[ab]" pattern and store it in $1
     5                 $y=uc($1);                       # change the case of $1 to upper-case and assign it to $y
     6                 $y=~s/-/_/;                      # replace the hyphen "-" by underscore "_" in $y
     7                 $x{$_}=$y                        # add (key,value) = (current_line, $y) in the hash %x
     8               }                                  # end of pattern match
     9             }                                    # end of processing "img.txt"
    10             elsif (/.*zoca_(.{7}).*/i) {         # at this point, we are *ALWAYS* processing "petdir.txt"; 
    11                                                  # so extract 7 characters after "zoca_" and store it in $1
    12               $y=uc($1);                         # change the case of $1 to upper-case and assign it to $y
    13               $y=~s/-/_/;                        # replace the hyphen "-" by underscore "_" in $y
    14               foreach $k (keys %x) {             # now we have to check if the current value of $y exists as a *key value*
    15                                                  # for any key in the hash %x; if it does, then set the *key value* to
    16                                                  # current line
    17                 if ($x{$k} eq $y) {              # if $y is the same as a *key value* for any key in %x, then
    18                   $x{$k} = $_                    # set that *key value* to current line (of "petdir.txt", that is)
    19                 }                                # done comparing *key value* to $y
    20               }                                  # done looping through the hash %x
    21             }                                    # done processing "petdir.txt"
    22             END {                                # we have the complete hash now. each key is a filename from "img.txt"
    23                                                  # and its corresponding value is the destination from "petdir.txt"
    24                                                  # and this correspondence was set due to the matching regexes
    25               foreach $k (keys %x) {             # now just loop through the hash and display "mv <key> <value>"
    26                 printf("mv %s %s\n",$k,$x{$k})
    27               }
    28             }' img.txt petdir.txt