Shell Programming and Scripting

 awk '
  BEGIN {                                                    ####### Start begin statement here.
    FS=" *; *"                                               ####### mentioning field seprator here as "*; *"  means it will take look for all text from starting to till semi colon as mentioned in your input file
    OFS=";"                                                  ####### mentioning output field seprator as semi colon ;
  } 
  FNR==1{                                                    ####### Whenever FNR is equal to 1, this condition will be TRUE whenever a new file read. As FNR will be reset whenever a new file is being read and on other hand NR will be keep on increasing it's value till all files being read.
    c++                                                      ####### incrementing the value of a variable named c by one.
  }
  c==1 {                                                     ####### When variable C's value is 1 this will be TRUE after first file is being read.
    A[$1]=$0                                                 ####### Creating an array named A whose index is $1 and value is $0 (complete line).
  } 
  c==2 {                                                     ####### When variable named C's value is 2 which will be TRUE when second file is being read because when read second file's turn will come then FNR==1 conditon will increase variable named C's value to 1 more which will be 2 now.
    A[$2]=A[$2] OFS $1                                       ####### Taking same array named A this time taking index as $2 because $1 of sampleouput1.txt and $2 of sampleoutput2.txt are same. Assigning the value to A{$2] OFS $1 where OFS is Output fielfd seprator.
  }
  c==3 {                                                     ####### When variable named C 's valie is 3 this will be TRUE when 3rd file is being read.
    $1=A[$1]                                                 ####### now making $1's value as A[$1]; because $1 of file named sampleoutput2.txt and $1 of sampleoutput1.txt and $2 of sampleoutput3.txt are same as per input files provided.
    print                                                    ####### Performing print action now, which will print complete line then.
  }
' sampleoutput1.txt sampleoutput3.txt sampleoutput2.txt      ####### mentioning filenames now.

awk -F ';' '
 FILENAME == ARGV[1] {A[$1] = ($2 ";" $3); next}
 FILENAME == ARGV[2] {A[$2] = A[$2] == "" ? (";;" $1) : (A[$2] ";" $1); next}
 FILENAME == ARGV[3] {A[$1] = A[$1] == "" ? (";;;" $2 ";" $3 ";" $4) : (A[$1] ";" $2 ";" $3 ";" $4)}
 END {for(x in A) print x ";" A[x]}' sampleoutput1.txt sampleoutput3.txt sampleoutput2.txt > sampleoutput1-2-3.txt

    FS=" *; *"                                               ####### using the field separator (FS) here as " *; *"  means it will consider spaces around the semicolons also part of the field separator (so that these spaces do not becomes part of the fields)