Shell Programming and Scripting

awk '/common-name/                                                                 ##### Searching for a string "common-name" here if any line contains this in it.
     {VAL=$2}                                                                      ##### setting variable named VAL's value to $2 here.
     /expiration/                                                                  ##### Searching for a string "expiration" here if any line contains this in it.
    {num=split("Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec", A,",");          ##### using split(built-in keyword of awk) to create an array named A, which has values of all the months Jan, Feb etc in it and mentioned separator as , in it.
    for(i=1;i<=num;i++){                                                           ##### starting a loop here which will start from i=1 to till the value of num(where num is the length of array A(which we created by split in above step)).
    B[A[i]]=i};                                                                    ##### creating an array B whose index is value of array A whose index is variable i, so it will be like B[A[1]]=B["Jan"]=1 and so on like this..
    print VAL FS $3"/"B[$2]"/"$(NF-1)                                              ##### printing the variable VAL here then mentioning FS(field seprator) which is space by default in awk. then printing values of $3"/"B[$2](where B[$2]' will be month's number)"/"$(NF-1)(is the second last field of each line, which is a year), which is date, month and year respectively.
   }'  Input_file                                                                  ##### Mentioning the Input_file here.