Ubuntu – Access individual lines of a text file and create separate text file with that name

Using awk

awk '!x[$0]++' infile.txt > outfile.txt

the way it works is that it keeps count of the lines in an array, and if the current count is zero, ie the first occurance, it prints the line, otherwise it continues to the next one.

You can do:

grep -Pzo '(?s)\n\K([^\n]*\n){3}[^\n]*command[^\n]*\n.*?\n[^\n]*ideal[^\n]*(?=\n)' file.txt

• -P enables Perl Compatible Regex, -z makes the input data separated on ASCII NUL rather than usual newline, -o lets up take only matched portion

• (?s) is DOTALL modifier, this enables us to match newline (\n) with . token

• \n\K([^\n]*\n){3} matches \n at first and then discards the match \K, ([^\n]*\n){3} matches three lines before line containing command

• [^\n]*command[^\n]*\n.*?\n[^\n]*ideal[^\n]*(?=\n) matches all lines starting from line having command till the line containing ideal

Example:

% cat file.txt
my name is
Mansour
and I confuse to
use sed
or grep for
piping my command output
to get 
my ideal output

% grep -Pzo '(?s)\n\K([^\n]*\n){3}[^\n]*command[^\n]*\n.*?\n[^\n]*ideal[^\n]*(?=\n)' file.txt
and I confuse to
use sed
or grep for
piping my command output
to get 
my ideal output