While reading Assuan commands, gpg-agent also allows a few special
commands to control its operation.  These control commands all start
with a slash (/).
     
/echo args/let name valueIf a variable is not found, it is searched in the environment and if found copied to the table of variables.
Variable functions are available: The name of the function must be followed by at least one space and the at least one argument. The following functions are available:
getcwdhomedirsysconfdirbindirlibdirlibexecdirdatadirserverpidunescape args\0 and
\x00 terminate the returned string implicitly.  The string to be
converted are the entire arguments right behind the delimiting space of
the function name.
          unpercent argsunpercent+ args%00
terminates the string implicitly.  The string to be converted are the
entire arguments right behind the delimiting space of the function
name. unpercent+ also maps plus signs to a spaces.
          percent argspercent+ argspercent+ also
maps spaces to plus signs.
          errcode argerrsource argerrstring argstrtol.  Return
the gpg-error error code, error source or a formatted string with the
error code and error source.
          +-*/%strtol and apply
this operator.  A division by zero yields an empty string.
          !|&strtol and apply
the logical oeprators NOT, OR or AND.  The NOT operator works on the
last argument only.
     /definq name var*) to match any inquiry.
     /definqfile name file*) to match any inquiry.
     /definqprog name prog/showdef/cleardef/sendfd file modefopen
mode string) and send the file descriptor to the server.  This is
usually followed by a command like INPUT FD to set the
input source for other commands.
     /recvfd/open var file [mode]/close fd/showopen/serverpid/sleep/hex/nohex/decode/nodecode/subst/nosubst/while condition/endwhile and the corresponding end are executed as long as
the evaluation of condition yields a non-zero value.  The
evaluation is done by passing condition to the strtol
function.  Example:
                 /subst
            /let i 3
            /while $i
              /echo loop couter is $i
              /let i ${- $i 1}
            /end
     /run file/bye/help