find(1) path/to/wikipages/ -type f -name "*.md" -print0 | shuf(1) --zero-terminated | head(1) -n500 --zero-terminated | xargs.1posix -0 -n1 -I{} cp "{}" .
search for files in a directory hierarchy
find [-H] [-L] [-P] [-D debugopts] [-Olevel] [path...] [expression]
-type c
       File is of type c:

       b      block (buffered) special

       c      character (unbuffered) special

       d      directory

       p      named pipe (FIFO)

       f      regular file

       l      symbolic link; this is never true if the -L option or the  -follow  option  is  in  effect,
              unless the symbolic link is broken.  If you want to search for symbolic links when -L is in
              effect, use -xtype.

       s      socket

       D      door (Solaris)
-name pattern
       Base of file name (the path with the leading directories removed) matches shell  pattern  pattern.
       The  metacharacters  (`*',  `?',  and  `[]')  match a `.' at the start of the base name (this is a
       change in findutils-4.2.2; see section STANDARDS CONFORMANCE below).  To ignore  a  directory  and
       the  files  under  it,  use  -prune;  see  an example in the description of -path.  Braces are not
       recognised as being special, despite the fact that some shells including Bash imbue braces with  a
       special  meaning  in  shell  patterns.   The  filename  matching  is performed with the use of the
       fnmatch(3) library function.   Don't forget to enclose the pattern in quotes in order  to  protect
       it from expansion by the shell.
       True;  print  the  full file name on the standard output, followed by a null character (instead of
       the newline character that -print uses).  This allows file names that contain  newlines  or  other
       types  of  white space to be correctly interpreted by programs that process the find output.  This
       option corresponds to the -0 option of xargs.
    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

    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).
generate random permutations
-z, --zero-terminated
       end lines with 0 byte, not newline
output the first part of files
-n, --lines=[-]K
       print  the  first  K lines instead of the first 10; with the leading `-', print all but the last K
       lines of each file
Print  the  first 10 lines of each FILE to standard output.  With more than one FILE, precede each with a
header giving the file name.  With no FILE, or when FILE is -, read standard input.
construct argument lists and invoke utility
-n  number
       Invoke utility using as many standard input arguments  as  possible,  up  to  number  (a  positive
       decimal integer) arguments maximum. Fewer arguments shall be used if:

        * The  command line length accumulated exceeds the size specified by the -s option (or {LINE_MAX}
          if there is no -s option).

        * The last iteration has fewer than number, but not zero, operands remaining.
-I  replstr
       Insert mode: utility is executed for each line from standard input, taking the entire  line  as  a
       single  argument,  inserting  it  in  arguments  for each occurrence of replstr. A maximum of five
       arguments in arguments can each contain one or more instances of  replstr.  Any  <blank>s  at  the
       beginning  of each line shall be ignored. Constructed arguments cannot grow larger than 255 bytes.
       Option -x shall be forced on.
source manpages: findshufheadxargs