Percol is an interactive grep tool in your terminal, commonly used with | (pipe concept on UNIX).

percol

• receives input lines from stdin or a file,
• lists up the input lines,
• waits for your input that filter/select the line(s),
• and finally outputs the selected line(s) to stdout. Since percol just filters the input and output the result to stdout, it can be used in command-chains with | in your shell (UNIX philosophy!).