Using awk command to display lines backwards - awk

Question

Fairly new to the awk command and still playing with it, I am trying to display multiple lines of a file, lets say lines 3-5, and display it backwards. So with the given file:
Hello World
How are you
I love computer science,
I am using awk,
And it is hard.
And it should output:
science, computer love I
awk, using am I
hard. is it And
Any step in the correct direction will be beneficial!!

Answer 1

Following awk may help you in same, where I am using start and end variables to get only those lines which are needed to be printed by OP.
awk -v start=3 -v end=5 'FNR>=start && FNR<=end{for(;NF>0;NF--){printf("%s%s",$NF,NF==1?RS:FS)}}' Input_file
Output will be as follows.
science, computer love I
awk, using am I
hard. is it And
Explanation: Adding explanation to solution too now.
awk -v start=3 -v end=5 ' ##Mentioning variables named start and end where start is denoting the starting line and end is denoting end line which we want to print.
FNR>=start && FNR<=end{ ##Checking condition here if variable FNR(awk out of the box variable) value is greater than or equal to variable start AND FNR value is less than or equal to end variable. If condition is TRUE then do following:
for(;NF>0;NF--){ ##Initiating a for loop which starts from value of NF(Number of fields, which is out of the box variable of awk) and it runs till NF is 0.
printf("%s%s",$NF,NF==1?RS:FS)} ##Printing value of NF(value of field) and other string will be either space of new line(by checking when field is first then print new line as print space).
}
' Input_file ##Mentioning Input_file name here.

Answer 2

$ cat tst.awk
NR>2 && NR<6 {
for (i=NF; i>0; i--) {
printf "%s%s", $i, (i>1?OFS:ORS)
}
}
$ awk -f tst.awk file
science, computer love I
awk, using am I
hard. is it And

Answer 3

You can use the following awk command to reach your goal:
input:
$ cat text
Hello World
How are you
I love computer science,
I am using awk,
And it is hard.
output:
$ awk 'NR<3{print}NR>=3{for(i=0; i<NF; i++){printf "%s ",$(NF-i);} printf "\n";}' text
Hello World
How are you
science, computer love I
awk, using am I
hard. is it And
Explanations:
NR<3{print} will print first 2 lines in the correct order
NR>=3{for(i=0; i<NF; i++){printf $(NF-i)" ";} printf "\n";}' from the 3rd line you have a loop on all the field identified by NF and you print them one after another from the last one to the first one ($NF is the last one $1 is the first one) and you separate each field with a space. Last but not least after the loop you print and EOL char.
Now, if you do not need to print the first 2 lines use:
$ awk 'NR>=3{for(i=0; i<NF; i++){printf "%s ",$(NF-i);} printf "\n";}' text
science, computer love I
awk, using am I
hard. is it And
For files with more lines for which you want to print only a range (3-5) use:
$ awk 'NR>=3 && NR<=5{for(i=0; i<NF; i++){printf "%s ",$(NF-i);} printf "\n";}' text