search for files in a directory hierarchy

find [-H] [-L] [-P] [-D debugopts] [-Olevel] [path...] [expression]

-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.

-exec command ;
       Execute  command;  true  if 0 status is returned.  All following arguments to find are taken to be
       arguments to the command until an argument consisting of `;' is encountered.  The string  `{}'  is
       replaced  by  the  current  file name being processed everywhere it occurs in the arguments to the
       command, not just in arguments where it is alone, as in some versions  of  find.   Both  of  these
       constructions  might  need  to be escaped (with a `\') or quoted to protect them from expansion by
       the shell.  See the EXAMPLES section for examples of the use of the -exec option.   The  specified
       command  is  run  once  for each matched file.  The command is executed in the starting directory.
       There are unavoidable security problems surrounding use of the -exec action; you  should  use  the
       -execdir option instead.

-exec command {} +
       This variant of the -exec action runs the specified command on the selected files, but the command
       line is built by appending each selected file name at the end; the total number of invocations  of
       the command will be much less than the number of matched files.  The command line is built in much
       the same way that xargs builds its command lines.  Only one instance of `{}' is allowed within the
       command.  The command is executed in the starting directory.

pattern-directed scanning and processing language

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).

sort lines of text files

-u, --unique
       with -c, check for strict ordering; without -c, output only the first of an equal run

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.