The non-interactive network downloader

Recursive Retrieval Options
    -r
    --recursive
        Turn on recursive retrieving.    The default maximum depth is 5.

--spider
    When invoked with this option, Wget will behave as a Web spider, which means that it will not
    download the pages, just check that they are there.  For example, you can use Wget to check your
    bookmarks:

            wget --spider --force-html -i bookmarks.html

    This feature needs much more work for Wget to get close to the functionality of real web spiders.

-l depth
--level=depth
    Specify recursion maximum depth level depth.

-t number
--tries=number
    Set number of retries to number.  Specify 0 or inf for infinite retrying.  The default is to retry 20
    times, with the exception of fatal errors like "connection refused" or "not found" (404), which are
    not retried.

Recursive Accept/Reject Options
    -A acclist --accept acclist
    -R rejlist --reject rejlist
        Specify comma-separated lists of file name suffixes or patterns to accept or reject. Note that if any
        of the wildcard characters, *, ?, [ or ], appear in an element of acclist or rejlist, it will be
        treated as a pattern, rather than a suffix.

wget [option]... [URL]...

Before a command is executed, its input and output may be redirected using a special notation interpreted
by  the  shell.   Redirection  may  also  be used to open and close files for the current shell execution
environment.  The following redirection operators may precede or appear anywhere within a simple  command
or may follow a command.  Redirections are processed in the order they appear, from left to right.

Redirecting Output
    Redirection of output causes the file whose name results from the expansion of  word  to  be  opened  for
    writing  on  file descriptor n, or the standard output (file descriptor 1) if n is not specified.  If the
    file does not exist it is created; if it does exist it is truncated to zero size.

    The general format for redirecting output is:

           [n]>word

    If the redirection operator is >, and the noclobber option to the  set  builtin  has  been  enabled,  the
    redirection  will  fail if the file whose name results from the expansion of word exists and is a regular
    file.  If the redirection operator is >|, or the redirection operator is > and the  noclobber  option  to
    the  set  builtin  command  is  not  enabled, the redirection is attempted even if the file named by word
    exists.

Pipelines
    A  pipeline is a sequence of one or more commands separated by one of the control operators | or |&.  The
    format for a pipeline is:

           [time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]

    The standard output of command is connected  via  a  pipe  to  the  standard  input  of  command2.   This
    connection  is performed before any redirections specified by the command (see REDIRECTION below).  If |&
    is used, the standard error of command is connected to command2's standard input through the pipe; it  is
    shorthand  for  2>&1  |.   This  implicit  redirection  of  the  standard  error  is  performed after any
    redirections specified by the command.

    The return status of a pipeline is the exit status of the last command, unless  the  pipefail  option  is
    enabled.   If  pipefail  is  enabled,  the  pipeline's return status is the value of the last (rightmost)
    command to exit with a non-zero status, or zero if all commands exit successfully.  If the reserved  word
    !   precedes  a  pipeline, the exit status of that pipeline is the logical negation of the exit status as
    described above.  The shell waits for all commands in the pipeline to terminate before returning a value.

    If the time reserved word precedes a pipeline, the elapsed as well as user and system  time  consumed  by
    its execution are reported when the pipeline terminates.  The -p option changes the output format to that
    specified by POSIX.  When the shell is in posix mode, it does not recognize time as a  reserved  word  if
    the  next  token begins with a `-'.  The TIMEFORMAT variable may be set to a format string that specifies
    how the timing information should be displayed; see the description of TIMEFORMAT under  Shell  Variables
    below.

    When the shell is in posix mode, time may be followed by a newline.  In this case, the shell displays the
    total user and system time consumed by the shell and its children.  The TIMEFORMAT variable may  be  used
    to specify the format of the time information.

    Each command in a pipeline is executed as a separate process (i.e., in a subshell).

print lines matching a pattern

Matcher Selection
    -E, --extended-regexp
           Interpret PATTERN as an extended regular expression (ERE, see below).  (-E is specified by POSIX.)

-i, --ignore-case
       Ignore case distinctions in both the PATTERN and the input files.  (-i is specified by POSIX.)

-o, --only-matching
       Print  only  the  matched  (non-empty) parts of a matching line, with each such part on a separate
       output line.

grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus
(-) is given as file name) for lines containing a match to the given PATTERN.  By  default,  grep  prints
the matching lines.

read from standard input and write to standard output and files

Copy standard input to each FILE, and also to standard output.

If a FILE is -, copy again to standard output.