Source_table_name  Source_col_name   Target_table_name    Target_col_name
Src_1@src_col11@Tgt_1@tgt_col11;
Src_2@src_col21@Tgt_2@tgt_col21;
......

Src_tbl       Tgt_tbl     join condition
Src_1@Tgt_1 @FROM ( SELECT SRC_1.* FROM SRC_1 INNER JOIN 
SRC_TEMP_1 ON  SRC_1.COL1=SRC_TEMP_1.COL1) SRC JOIN (SELECT 
TGT_1.* FROM TGT_1   INNER JOIN TGT_TEMP_1 ON 
TGT_1.COL1=TGT_TEMP_1.COL1) TGT ON   SRC.COL1=TGT.COL1;
Src_2@Tgt_2@FROM( SELECT SRC_2.*  FROM SRC_2 LEFT OUTER JOIN TGT_2 ON SRC_2.COL1=TGT_2.COL1;

awk -F[@] 'BEGIN { RS=";"  OFS=" "}
FNR==NR{src_tgt_array[$1 OFS $3]="something";
next;
}
{
join_array[$1 OFS $2]=$3
}
end {
for (i in src_tgt_array)
{
print "src and tgt tables " i " join condition is " join_array[i]
print "----------------"
} 
}' < file1.txt file2.txt > awk_output.txt

src and tgt tables Src_1 Tgt_1 join condition is FROM ( SELECT SRC_1.*
 FROM SRC_1 INNER JOIN SRC_TEMP_1 ON  SRC_1.COL1=SRC_TEMP_1.COL1) SRC
 JOIN (SELECT TGT_1.* FROM TGT_1   INNER JOIN TGT_TEMP_1 ON TGT_1.COL1=TGT_TEMP_1.COL1) TGT 
ON   SRC.COL1=TGT.COL1
----------------
src and tgt tables 
Src_2 Tgt_2 join condition is 
----------------

src and tgt tables Src_1 Tgt_1 join condition is FROM ( SELECT SRC_1.* FROM SRC_1 INNER JOIN SRC_TEMP_1 ON  SRC_1.COL1=SRC_TEMP_1.COL1) SRC 
JOIN (SELECT TGT_1.* FROM TGT_1   INNER JOIN TGT_TEMP_1 ON TGT_1.COL1=TGT_TEMP_1.COL1) TGT 
ON   SRC.COL1=TGT.COL1
----------------

src and tgt tables Src_2 Tgt_2 join condition is FROM( SELECT SRC_2.*  FROM SRC_2 
LEFT OUTER JOIN TGT_2 ON SRC_2.COL1=TGT_2.COL1
----------------