for pool in $(zpool list -Hg -o name) ; do log_file="${HOME}/deletion-${pool}.log"; rm.1posix -f "${log_file}" && for i in $(zfs list -t snapshot | grep "^${pool}" | grep 'zfs-auto-snap'| awk '{print $1}') ; do sudo(8) zfs destroy -v "$i" | plan9-tee.1 -a "${log_file}" ; done ; done
for name [ [ in [ word ... ] ] ; ] do list ; done
       The  list of words following in is expanded, generating a list of items.  The variable name is set
       to each element of this list in turn, and list is executed each time.  If the in word is  omitted,
       the  for  command  executes  list  once  for each positional parameter that is set (see PARAMETERS
       below).  The return status is the exit status of the last command that executes.  If the expansion
       of  the  items  following  in  results  in an empty list, no commands are executed, and the return
       status is 0.
A variable may be assigned to by a statement of the form

       name=[value]

If value is not given, the variable is assigned the null string.  All  values  undergo  tilde  expansion,
parameter  and  variable  expansion,  command  substitution, arithmetic expansion, and quote removal (see
EXPANSION below).  If the variable has  its  integer  attribute  set,  then  value  is  evaluated  as  an
arithmetic  expression even if the $((...)) expansion is not used (see Arithmetic Expansion below).  Word
splitting is not performed, with the exception of "$@"  as  explained  below  under  Special  Parameters.
Pathname  expansion  is  not performed.  Assignment statements may also appear as arguments to the alias,
declare, typeset, export, readonly, and local builtin commands.

In the context where an assignment statement is assigning a value to a shell variable or array index, the
+=  operator  can  be used to append to or add to the variable's previous value.  When += is applied to a
variable for which the integer attribute has been set, value is evaluated as an arithmetic expression and
added  to the variable's current value, which is also evaluated.  When += is applied to an array variable
using compound assignment (see Arrays below), the variable's value is not unset (as it is when using  =),
and  new  values  are  appended to the array beginning at one greater than the array's maximum index (for
indexed arrays) or added as additional key-value pairs in  an  associative  array.   When  applied  to  a
string-valued variable, value is expanded and appended to the variable's value.
remove directory entries
-f     Do not prompt for confirmation. Do not write diagnostic messages or modify the exit status in  the
       case of nonexistent operands.  Any previous occurrences of the -i option shall be ignored.
AND and OR lists are sequences of one of more pipelines separated by the &&  and  ||  control  operators,
respectively.  AND and OR lists are executed with left associativity.  An AND list has the form

       command1 && command2

command2 is executed if, and only if, command1 returns an exit status of zero.

An OR list has the form

       command1 || command2

command2  is  executed  if and only if command1 returns a non-zero exit status.  The return status of AND
and OR lists is the exit status of the last command executed in the list.
execute a command as another user
sudo allows a permitted user to execute a command as the superuser or another user, as specified by the
security policy.  The real and effective uid and gid are set to match those of the target user, as
specified in the password database, and the group vector is initialized based on the group database
(unless the -P option was specified).
-v          When given the -v (validate) option, sudo will update the user's cached credentials,
            authenticating the user's password if necessary.  For the sudoers plugin, this extends the
            sudo timeout for another 15 minutes (or whatever the timeout is set to in sudoers) but does
            not run a command.  Not all security policies support cached credentials.
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).
pipe fitting
-a     Append the output to the files rather than rewriting them.
source manpages: rmsudoplan9-tee