UNIX for Beginners Questions & Answers

awk '/OH|RU|OI/    ####So here we are searching for lines which have strings "OH" or "RU" or "OI", if yes then do following operations.
{sub(/^ +/,X,$0);  ####Here I am using awk's built-in substitute functionality by using sub, whose syntax is--> sub(/pattern or value which needs to be substituted/,new_value,line/variable), so here 
                       I am substituting each line which is starting with space by doing (^ ) with X(a variable) whose value is NULL in current line/record by mentioning $0.
print}             ####printing line here, so either previous line's leading spaces were removed or not print will happen(as per your shown code only prepared it) in both the cases.
';