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#### 7.8.2 Control commands.

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
  Just print args.
`/let` name value
  Set the variable name to value. Variables are only substituted on the input if the `/subst` has been used. Variables are referenced by prefixing the name with a dollar sign and optionally include the name in curly braces. The rules for a valid name are identically to those of the standard bourne shell. This is not yet enforced but may be in the future. When used with curly braces no leading or trailing white space is allowed.

  If 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:

  `get`
    Return a value described by the argument. Available arguments are:
    `cwd`
      The current working directory.
    `homedir`
      The gnupg homedir.
    `sysconfdir`
      GnuPG's system configuration directory.
    `bindir`
      GnuPG's binary directory.
    `libdir`
      GnuPG's library directory.
    `libexecdir`
      GnuPG's library directory for executable files.
    `datadir`
      GnuPG's data directory.
    `serverpid`
      The PID of the current server. Command `/serverpid` must have been given to return a useful value.
  `unescape` args
    Remove C-style escapes from args. Note that `\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` args
  `unpercent+` args
    Remove percent style escaping from args. Note that `%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` args
  `percent+` args
    Escape the args using percent style escaping. Tabs, formfeeds, linefeeds, carriage returns and colons are escaped. `percent+` also maps spaces to plus signs.
  `errcode` arg
  `errsource` arg
  `errstring` arg
    Assume arg is an integer and evaluate it using `strtol`. Return the gpg-error error code, error source or a formatted string with the error code and error source.
  `+`
  `-`
  `*`
  `/`
  `%`
    Evaluate all arguments as long integers using `strtol` and apply this operator. A division by zero yields an empty string.
  `!`
  `|`
  `&`
    Evaluate all arguments as long integers using `strtol` and apply the logical oeprators NOT, OR or AND. The NOT operator works on the last argument only.
`/definq` name var
  Use content of the variable var for inquiries with name. name may be an asterisk (`*`) to match any inquiry.
`/definqfile` name file
  Use content of file for inquiries with name. name may be an asterisk (`*`) to match any inquiry.
`/definqprog` name prog
  Run prog for inquiries matching name and pass the entire line to it as command line arguments.
`/datafile` name
  Write all data lines from the server to the file name. The file is opened for writing and created if it does not exists. An existing file is first truncated to 0. The data written to the file fully decoded. Using a single dash for name writes to stdout. The file is kept open until a new file is set using this command or this command is used without an argument.
`/showdef`
  Print all definitions
`/cleardef`
  Delete all definitions
`/sendfd` file mode
  Open file in mode (which needs to be a valid `fopen` 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`
  Not yet implemented.
`/open` var file`[`mode`]`
  Open file and assign the file descriptor to var. Warning: This command is experimental and might change in future versions.
`/close` fd
  Close the file descriptor fd. Warning: This command is experimental and might change in future versions.
`/showopen`
  Show a list of open files.
`/serverpid`
  Send the Assuan command `GETINFO pid` to the server and store the returned PID for internal purposes.
`/sleep`
  Sleep for a second.
`/hex`
`/nohex`
  Same as the command line option `--hex`.
`/decode`
`/nodecode`
  Same as the command line option `--decode`.
`/subst`
`/nosubst`
  Enable and disable variable substitution. It defaults to disabled unless the command line option `--subst` has been used. If /subst as been enabled once, leading whitespace is removed from input lines which makes scripts easier to read.
`/while` condition
`/end`
  These commands provide a way for executing loops. All lines between the `while` and the corresponding `end` are executed as long as the evaluation of condition yields a non-zero value or is the string `true` or `yes`. 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

`/if` condition
`/end`
  These commands provide a way for conditional execution. All lines between the `if` and the corresponding `end` are executed only if the evaluation of condition yields a non-zero value or is the string `true` or `yes`. The evaluation is done by passing condition to the `strtol` function.
`/run` file
  Run commands from file.
`/bye`
  Terminate the connection and the program
`/help`
  Print a list of available control commands.