Answer by Quasímodo for Show all lines before a match

• Including the match,

  sed '/foo/q' file

  It is better to quit sed as soon as a match is found, otherwise sed would keep reading the file and wasting your time, which would be considerable for large files.

• Excluding the match,

  sed -n '/foo/q;p' file

  The -n flag means that only lines that reach the p command will be printed. Since the foo line triggers the quit action, it does not reach p and thus is not printed.

  • If your sed is GNU's, this can be simplified to

    sed '/foo/Q' file

References

1. /foo/—Addresses
2. q, p—Often-used commands
3. Q—GNU Sed extended commands
4. -n—Command-line options