Supposing I have a file named sample.txt which contains data in the following format:
1 John 2 Crema 3 Abraham 1 John I can read the file line by line using the following way:
while read p do echo $p done <sample.txt Is there any way that I can compare a particular line with its following lines so that I can perform multiple task such as duplicate elimination or pattern matching, etc? What additional things will I have to add to accomplish the comparison task?
prev="" while read p; do # compare p with prev somehow prev="$p" done <sample.txt This allows you to compare any two directly adjacent lines. If you want to compare lines further apart in the file, it becomes more complicated and may not be best written in shell (though the specific details will vary based on the task).
awk '{if (NR==1) STR=$0; if ($0==STR) print NR}' file In this case I use line number 1 as basis for comparison. Modify NR==1 to whichever line number you want to compare to.
It will print all line numbers which match the selected line, including the selected line. Applied to your example it will print:
1
4
Once you have line numbers, you can eliminate them via e.g. sed:
sed -i '4d' file Or perform other tasks on those lines (e.g. further awk with NR=line number)
