catenate files

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).

translate or delete characters

-d, --delete
       delete characters in SET1, do not translate

tr [OPTION]... SET1 [SET2]

Translate, squeeze, and/or delete characters from standard input, writing to standard output.

SETs are specified as strings of characters.  Most represent themselves.  Interpreted sequences are:

\NNN   character with octal value NNN (1 to 3 octal digits)

\\     backslash

\a     audible BEL

\b     backspace

\f     form feed

\n     new line

\r     return

\t     horizontal tab

\v     vertical tab

CHAR1-CHAR2
       all characters from CHAR1 to CHAR2 in ascending order

[CHAR*]
       in SET2, copies of CHAR until length of SET1

[CHAR*REPEAT]
       REPEAT copies of CHAR, REPEAT octal if starting with 0

[:alnum:]
       all letters and digits

[:alpha:]
       all letters

[:blank:]
       all horizontal whitespace

[:cntrl:]
       all control characters

[:digit:]
       all digits

[:graph:]
       all printable characters, not including space

[:lower:]
       all lower case letters

[:print:]
       all printable characters, including space

[:punct:]
       all punctuation characters

[:space:]
       all horizontal or vertical whitespace

[:upper:]
       all upper case letters

[:xdigit:]
       all hexadecimal digits

[=CHAR=]
       all characters which are equivalent to CHAR

while list-1; do list-2; done
until list-1; do list-2; done
       The while command continuously executes the list list-2 as long as the last command  in  the  list
       list-1  returns  an  exit  status  of  zero.  The until command is identical to the while command,
       except that the test is negated; list-2 is executed as long as the last command in list-1  returns
       a non-zero exit status.  The exit status of the while and until commands is the exit status of the
       last command executed in list-2, or zero if none was executed.

read a line from standard input

The non-interactive network downloader

-O file
--output-document=file
    The documents will not be written to the appropriate files, but all will be concatenated together and
    written to file.  If - is used as file, documents will be printed to standard output, disabling link
    conversion.  (Use ./- to print to a file literally named -.)

    Use of -O is not intended to mean simply "use the name file instead of the one in the URL;" rather,
    it is analogous to shell redirection: wget -O file http://foo is intended to work like wget -O -
    http://foo > file; file will be truncated immediately, and all downloaded content will be written
    there.

    For this reason, -N (for timestamp-checking) is not supported in combination with -O: since file is
    always newly created, it will always have a very new timestamp. A warning will be issued if this
    combination is used.

    Similarly, using -r or -p with -O may not work as you expect: Wget won't just download the first file
    to file and then download the rest to their normal names: all downloaded content will be placed in
    file. This was disabled in version 1.11, but has been reinstated (with a warning) in 1.11.2, as there
    are some cases where this behavior can actually have some use.

    Note that a combination with -k is only permitted when downloading a single document, as in that case
    it will just convert all relative URIs to external ones; -k makes no sense for multiple URIs when
    they're all being downloaded to a single file; -k can be used only when the output is a regular file.

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