sed command to replace a line in a file using line number from the output of a pipe.

Shell Programming and Scripting
1

Sed command to replace a line in a file using line number from the output of a pipe.

Is it possible to replace a whole line piped from someother command into a file at paritcular line...

here is some basic execution flow..

the line number is 412
lineNo=412

Now i have a line coming as output from another command. for simplicity lets say i am
displaying contents of a file at particular line number

cat fileName.txt |  sed -n ${lineNo}p  | some sed replacement command goes here | "HERE SHOULD BE MY SED COMMAND which should replace the line 412 with the input got from previous command.

Is it feasible?

If not is there a way to output the command to a file(which obviously will have only one line) then take this as input and replace it at line 412 in the original fileName.txt file.

2 
lineNo=412
var=$(whatever_you_want_line_412_to_be)
sed -i "${lineNo}s/.*/$var/" filename.txt

Careful while using -i switch of sed to perform an in-place editing.