sed command

$> sed
Usage: sed [OPTION]... {script-only-if-no-other-script} [input-file]...

  -n, --quiet, --silent
                 suppress automatic printing of pattern space
  -e script, --expression=script
                 add the script to the commands to be executed
  -f script-file, --file=script-file
                 add the contents of script-file to the commands to be executed
  --follow-symlinks
                 follow symlinks when processing in place
  -i[SUFFIX], --in-place[=SUFFIX]
                 edit files in place (makes backup if SUFFIX supplied)
  -l N, --line-length=N
                 specify the desired line-wrap length for the `l' command
  --posix
                 disable all GNU extensions.
  -r, --regexp-extended
                 use extended regular expressions in the script.
  -s, --separate
                 consider files as separate rather than as a single continuous
                 long stream.
  -u, --unbuffered
                 load minimal amounts of data from the input files and flush
                 the output buffers more often
  -z, --null-data
                 separate lines by NUL characters
      --help     display this help and exit
      --version  output version information and exit

If no -e, --expression, -f, or --file option is given, then the first
non-option argument is taken as the sed script to interpret.  All
remaining arguments are names of input files; if no input files are
specified, then the standard input is read.

GNU sed home page: <http://www.gnu.org/software/sed/>.
General help using GNU software: <http://www.gnu.org/gethelp/>.

$> tldr sed

  sed

  Edit text in a scriptable manner.

  - Replace the first occurrence of a regular expression in each line of a file, and print the result:
    sed 's/regex/replace/' filename

  - Replace all occurrences of an extended regular expression in a file, and print the result:
    sed -r 's/regex/replace/g' filename

  - Replace all occurrences of a string in a file, overwriting the file (i.e. in-place):
    sed -i 's/find/replace/g' filename

  - Replace only on lines matching the line pattern:
    sed '/line_pattern/s/find/replace/' filename

  - Delete lines matching the line pattern:
    sed '/line_pattern/d' filename

  - Print only text between n-th line till the next empty line:
    sed -n 'n,/^$/p' filename

  - Apply multiple find-replace expressions to a file:
    sed -e 's/find/replace/' -e 's/find/replace/' filename

  - Replace separator / by any other character not used in the find or replace patterns, e.g., #:
    sed 's#find#replace#' filename

  - Print only the n-th line of a file:
    sed 'nq;d' filename