How to compare and substitute strings in different lines in unix

Question

I want to compare and substitute strings present in different lines in unix

For example I have a file with two words in each line

Answer 1

This is VERY clearly a case for a recursive descent solution:

$ cat tst.awk
function descend(node) {return (map[node] in map ? descend(map[node]) : map[node])}
{ map[$1] = $2 }
END { for (key in map) print key, descend(key) }

$ awk -f tst.awk file
 
 
 
 

If infinite recursion in your input is a possibility, here;s an approach that will print as the 2nd field the last node before the recursion starts and put a "*" next to it so you know it's happening:

$ cat tst.awk
function descend(node,  child, descendant) {
    stack[node]
    child = map[node]
    if (child in map) {
        if (child in stack) {
            descendant = node "*"
        }
        else {
            descendant = descend(child)
        }
    }
    else {
        descendant = child
    }
    delete stack[node]
    return descendant
}
{ map[$1] = $2 }
END { for (key in map) print key, descend(key) }

.

$ cat file
 
 
 
 
 
 
 
 

$ awk -f tst.awk file
 *
 *
 *
 *
 
 
 
 

If you need the output order to match the input order and/or or to print duplicate lines twice, change the bottom 2 lines of the script to:

{ keys[++numKeys] = $1; map[$1] = $2 }
END {
    for (keyNr=1; keyNr<=numKeys; keyNr++) {
        key = keys[keyNr]
        print key, descend(key)
    }
}