Telnet

Library version:3.0.4
Library scope:test suite
Named arguments:supported

Introduction

A test library providing communication over Telnet connections.

Telnet is Robot Framework's standard library that makes it possible to connect to Telnet servers and execute commands on the opened connections.

Table of contents

Connections

The first step of using Telnet is opening a connection with Open Connection keyword. Typically the next step is logging in with Login keyword, and in the end the opened connection can be closed with Close Connection.

It is possible to open multiple connections and switch the active one using Switch Connection. Close All Connections can be used to close all the connections, which is especially useful in suite teardowns to guarantee that all connections are always closed.

Writing and reading

After opening a connection and possibly logging in, commands can be executed or text written to the connection for other reasons using Write and Write Bare keywords. The main difference between these two is that the former adds a configurable newline after the text automatically.

After writing something to the connection, the resulting output can be read using Read, Read Until, Read Until Regexp, and Read Until Prompt keywords. Which one to use depends on the context, but the latest one is often the most convenient.

As a convenience when running a command, it is possible to use Execute Command that simply uses Write and Read Until Prompt internally. Write Until Expected Output is useful if you need to wait until writing something produces a desired output.

Written and read text is automatically encoded/decoded using a configured encoding.

The ANSI escape codes, like cursor movement and color codes, are normally returned as part of the read operation. If an escape code occurs in middle of a search pattern it may also prevent finding the searched string. Terminal emulation can be used to process these escape codes as they would be if a real terminal would be in use.

Configuration

Many aspects related the connections can be easily configured either globally or per connection basis. Global configuration is done when library is imported, and these values can be overridden per connection by Open Connection or with setting specific keywords Set Timeout, Set Newline, Set Prompt, Set Encoding, Set Default Log Level and Set Telnetlib Log Level.

Values of environ_user, window_size, terminal_emulation, and terminal_type can not be changed after opening the connection.

Timeout

Timeout defines how long is the maximum time to wait when reading output. It is used internally by Read Until, Read Until Regexp, Read Until Prompt, and Login keywords. The default value is 3 seconds.

Connection Timeout

Connection Timeout defines how long is the maximum time to wait when opening the telnet connection. It is used internally by Open Connection. The default value is the system global default timeout.

New in Robot Framework 2.9.2.

Newline

Newline defines which line separator Write keyword should use. The default value is CRLF that is typically used by Telnet connections.

Newline can be given either in escaped format using \n and \r or with special LF and CR syntax.

Examples:

Set Newline \n
Set Newline CRLF

Prompt

Often the easiest way to read the output of a command is reading all the output until the next prompt with Read Until Prompt. It also makes it easier, and faster, to verify did Login succeed.

Prompt can be specified either as a normal string or a regular expression. The latter is especially useful if the prompt changes as a result of the executed commands. Prompt can be set to be a regular expression by giving prompt_is_regexp argument a true value (see Boolean arguments).

Examples:

Open Connection lolcathost prompt=$
Set Prompt (> |# ) prompt_is_regexp=true

Encoding

To ease handling text containing non-ASCII characters, all written text is encoded and read text decoded by default. The default encoding is UTF-8 that works also with ASCII. Encoding can be disabled by using a special encoding value NONE. This is mainly useful if you need to get the bytes received from the connection as-is.

Notice that when writing to the connection, only Unicode strings are encoded using the defined encoding. Byte strings are expected to be already encoded correctly. Notice also that normal text in test data is passed to the library as Unicode and you need to use variables to use bytes.

It is also possible to configure the error handler to use if encoding or decoding characters fails. Accepted values are the same that encode/decode functions in Python strings accept. In practice the following values are the most useful:

Examples:

Open Connection lolcathost encoding=Latin1 encoding_errors=strict
Set Encoding ISO-8859-15
Set Encoding errors=ignore

Using UTF-8 encoding by default and being able to configure the encoding are new features in Robot Framework 2.7.6. In earlier versions only ASCII was supported and encoding errors were silently ignored. Robot Framework 2.7.7 added a possibility to specify the error handler, changed the default behavior back to ignoring encoding errors, and added the possibility to disable encoding.

Default log level

Default log level specifies the log level keywords use for logging unless they are given an explicit log level. The default value is INFO, and changing it, for example, to DEBUG can be a good idea if there is lot of unnecessary output that makes log files big.

Configuring default log level in importing and with Open Connection are new features in Robot Framework 2.7.6. In earlier versions only Set Default Log Level could be used.

Terminal type

By default the Telnet library does not negotiate any specific terminal type with the server. If a specific terminal type, for example vt100, is desired, the terminal type can be configured in importing and with Open Connection.

New in Robot Framework 2.8.2.

Window size

Window size for negotiation with the server can be configured when importing the library and with Open Connection.

New in Robot Framework 2.8.2.

USER environment variable

Telnet protocol allows the USER environment variable to be sent when connecting to the server. On some servers it may happen that there is no login prompt, and on those cases this configuration option will allow still to define the desired username. The option environ_user can be used in importing and with Open Connection.

New in Robot Framework 2.8.2.

Terminal emulation

Starting from Robot Framework 2.8.2, Telnet library supports terminal emulation with Pyte. Terminal emulation will process the output in a virtual screen. This means that ANSI escape codes, like cursor movements, and also control characters, like carriage returns and backspaces, have the same effect on the result as they would have on a normal terminal screen. For example the sequence acdc\x1b[3Dbba will result in output abba.

Terminal emulation is taken into use by giving terminal_emulation argument a true value (see Boolean arguments) either in the library initialization or with Open Connection.

As Pyte approximates vt-style terminal, you may also want to set the terminal type as vt100. We also recommend that you increase the window size, as the terminal emulation will break all lines that are longer than the window row length.

When terminal emulation is used, the newline and encoding can not be changed anymore after opening the connection.

Examples:

Open Connection lolcathost terminal_emulation=True terminal_type=vt100 window_size=400x100

As a prerequisite for using terminal emulation, you need to have Pyte installed. Due to backwards incompatible changes in Pyte, different Robot Framework versions support different Pyte versions:

Logging

All keywords that read something log the output. These keywords take the log level to use as an optional argument, and if no log level is specified they use the configured default value.

The valid log levels to use are TRACE, DEBUG, INFO (default), and WARN. Levels below INFO are not shown in log files by default whereas warnings are shown more prominently.

The telnetlib module used by this library has a custom logging system for logging content it sends and receives. By default these messages are written using TRACE level. Starting with Robot Framework 2.8.7 the level is configurable with the telnetlib_log_level option either in the library initialization, to the Open Connection or by using the Set Telnetlib Log Level keyword to the active connection. Special level NONE con be used to disable the logging altogether.

Time string format

Timeouts and other times used must be given as a time string using format like 15 seconds or 1min 10s. If the timeout is given as just a number, for example, 10 or 1.5, it is considered to be seconds. The time string format is described in more detail in an appendix of Robot Framework User Guide.

Boolean arguments

Some keywords accept arguments that are handled as Boolean values true or false. If such an argument is given as a string, it is considered false if it is either an empty string or case-insensitively equal to false, none or no. Other strings are considered true regardless their value, and other argument types are tested using the same rules as in Python.

True examples:

Open Connection lolcathost terminal_emulation=True # Strings are generally true.
Open Connection lolcathost terminal_emulation=yes # Same as the above.
Open Connection lolcathost terminal_emulation=${TRUE} # Python True is true.
Open Connection lolcathost terminal_emulation=${42} # Numbers other than 0 are true.

False examples:

Open Connection lolcathost terminal_emulation=False # String false is false.
Open Connection lolcathost terminal_emulation=no # Also string no is false.
Open Connection lolcathost terminal_emulation=${EMPTY} # Empty string is false.
Open Connection lolcathost terminal_emulation=${FALSE} # Python False is false.

Prior to Robot Framework 2.9, all non-empty strings, including false and no, were considered to be true. Considering none false is new in Robot Framework 3.0.3.

Importing

Arguments Documentation
timeout=3 seconds, newline=CRLF, prompt=None, prompt_is_regexp=False, encoding=UTF-8, encoding_errors=ignore, default_log_level=INFO, window_size=None, environ_user=None, terminal_emulation=False, terminal_type=None, telnetlib_log_level=TRACE, connection_timeout=None

Telnet library can be imported with optional configuration parameters.

Configuration parameters are used as default values when new connections are opened with Open Connection keyword. They can also be overridden after opening the connection using the Set ... keywords. See these keywords as well as Configuration, Terminal emulation and Logging sections above for more information about these parameters and their possible values.

See Time string format and Boolean arguments sections for information about using arguments accepting times and Boolean values, respectively.

Examples (use only one of these):

Setting Value Value Value Value Comment
Library Telnet # default values
Library Telnet 5 seconds # set only timeout
Library Telnet newline=LF encoding=ISO-8859-1 # set newline and encoding using named arguments
Library Telnet prompt=$ # set prompt
Library Telnet prompt=(> |# ) prompt_is_regexp=yes # set prompt as a regular expression
Library Telnet terminal_emulation=True terminal_type=vt100 window_size=400x100 # use terminal emulation with defined window size and terminal type
Library Telnet telnetlib_log_level=NONE # disable logging messages from the underlying telnetlib

Shortcuts

Close All Connections · Close Connection · Execute Command · Login · Open Connection · Read · Read Until · Read Until Prompt · Read Until Regexp · Set Default Log Level · Set Encoding · Set Newline · Set Prompt · Set Telnetlib Log Level · Set Timeout · Switch Connection · Write · Write Bare · Write Control Character · Write Until Expected Output

Keywords

Keyword Arguments Documentation
Close All Connections

Closes all open connections and empties the connection cache.

If multiple connections are opened, this keyword should be used in a test or suite teardown to make sure that all connections are closed. It is not an error is some of the connections have already been closed by Close Connection.

After this keyword, new indexes returned by Open Connection keyword are reset to 1.
Close Connection loglevel=None

Closes the current Telnet connection.

Remaining output in the connection is read, logged, and returned. It is not an error to close an already closed connection.

Use Close All Connections if you want to make sure all opened connections are closed.

See Logging section for more information about log levels.
Execute Command command, loglevel=None, strip_prompt=False

Executes the given command and reads, logs, and returns everything until the prompt.

This keyword requires the prompt to be configured either in importing or with Open Connection or Set Prompt keyword.

This is a convenience keyword that uses Write and Read Until Prompt internally. Following two examples are thus functionally identical:

${out} = Execute Command pwd
Write pwd
${out} = Read Until Prompt

See Logging section for more information about log levels and Read Until Prompt for more information about the strip_prompt parameter.
Login username, password, login_prompt=login: , password_prompt=Password: , login_timeout=1 second, login_incorrect=Login incorrect

Logs in to the Telnet server with the given user information.

This keyword reads from the connection until the login_prompt is encountered and then types the given username. Then it reads until the password_prompt and types the given password. In both cases a newline is appended automatically and the connection specific timeout used when waiting for outputs.

How logging status is verified depends on whether a prompt is set for this connection or not:

1) If the prompt is set, this keyword reads the output until the prompt is found using the normal timeout. If no prompt is found, login is considered failed and also this keyword fails. Note that in this case both login_timeout and login_incorrect arguments are ignored.

2) If the prompt is not set, this keywords sleeps until login_timeout and then reads all the output available on the connection. If the output contains login_incorrect text, login is considered failed and also this keyword fails. Both of these configuration parameters were added in Robot Framework 2.7.6. In earlier versions they were hard coded.

See Configuration section for more information about setting newline, timeout, and prompt.
Open Connection host, alias=None, port=23, timeout=None, newline=None, prompt=None, prompt_is_regexp=False, encoding=None, encoding_errors=None, default_log_level=None, window_size=None, environ_user=None, terminal_emulation=None, terminal_type=None, telnetlib_log_level=None, connection_timeout=None

Opens a new Telnet connection to the given host and port.

The timeout, newline, prompt, prompt_is_regexp, encoding, default_log_level, window_size, environ_user, terminal_emulation, terminal_type and telnetlib_log_level arguments get default values when the library is imported. Setting them here overrides those values for the opened connection. See Configuration, Terminal emulation and Logging sections for more information about these parameters and their possible values.

Possible already opened connections are cached and it is possible to switch back to them using Switch Connection keyword. It is possible to switch either using explicitly given alias or using index returned by this keyword. Indexing starts from 1 and is reset back to it by Close All Connections keyword.
Read loglevel=None

Reads everything that is currently available in the output.

Read output is both returned and logged. See Logging section for more information about log levels.
Read Until expected, loglevel=None

Reads output until expected text is encountered.

Text up to and including the match is returned and logged. If no match is found, this keyword fails. How much to wait for the output depends on the configured timeout.

See Logging section for more information about log levels. Use Read Until Regexp if more complex matching is needed.
Read Until Prompt loglevel=None, strip_prompt=False

Reads output until the prompt is encountered.

This keyword requires the prompt to be configured either in importing or with Open Connection or Set Prompt keyword.

By default, text up to and including the prompt is returned and logged. If no prompt is found, this keyword fails. How much to wait for the output depends on the configured timeout.

If you want to exclude the prompt from the returned output, set strip_prompt to a true value (see Boolean arguments). If your prompt is a regular expression, make sure that the expression spans the whole prompt, because only the part of the output that matches the regular expression is stripped away.

See Logging section for more information about log levels.

Optionally stripping prompt is a new feature in Robot Framework 2.8.7.
Read Until Regexp *expected

Reads output until any of the expected regular expressions match.

This keyword accepts any number of regular expressions patterns or compiled Python regular expression objects as arguments. Text up to and including the first match to any of the regular expressions is returned and logged. If no match is found, this keyword fails. How much to wait for the output depends on the configured timeout.

If the last given argument is a valid log level, it is used as loglevel similarly as with Read Until keyword.

See the documentation of Python re module for more information about the supported regular expression syntax. Notice that possible backslashes need to be escaped in Robot Framework test data.

Examples:

Read Until Regexp (#|$)
Read Until Regexp first_regexp second_regexp
Read Until Regexp \\d{4}-\\d{2}-\\d{2} DEBUG
Set Default Log Level level

Sets the default log level used for logging in the current connection.

The old default log level is returned and can be used to restore the log level later.

See Configuration section for more information about global and connection specific configuration.
Set Encoding encoding=None, errors=None

Sets the encoding to use for writing and reading in the current connection.

The given encoding specifies the encoding to use when written/read text is encoded/decoded, and errors specifies the error handler to use if encoding/decoding fails. Either of these can be omitted and in that case the old value is not affected. Use string NONE to disable encoding altogether.

See Configuration section for more information about encoding and error handlers, as well as global and connection specific configuration in general.

The old values are returned and can be used to restore the encoding and the error handler later. See Set Prompt for a similar example.

If terminal emulation is used, the encoding can not be changed on an open connection.

Setting encoding in general is a new feature in Robot Framework 2.7.6. Specifying the error handler and disabling encoding were added in 2.7.7.
Set Newline newline

Sets the newline used by Write keyword in the current connection.

The old newline is returned and can be used to restore the newline later. See Set Timeout for a similar example.

If terminal emulation is used, the newline can not be changed on an open connection.

See Configuration section for more information about global and connection specific configuration.
Set Prompt prompt, prompt_is_regexp=False

Sets the prompt used by Read Until Prompt and Login in the current connection.

If prompt_is_regexp is given a true value (see Boolean arguments), the given prompt is considered to be a regular expression.

The old prompt is returned and can be used to restore the prompt later.

Example:

${prompt} ${regexp} = Set Prompt $
Do Something
Set Prompt ${prompt} ${regexp}

See the documentation of Python re module for more information about the supported regular expression syntax. Notice that possible backslashes need to be escaped in Robot Framework test data.

See Configuration section for more information about global and connection specific configuration.
Set Telnetlib Log Level level

Sets the log level used for logging in the underlying telnetlib.

Note that telnetlib can be very noisy thus using the level NONE can shutdown the messages generated by this library.

New in Robot Framework 2.8.7.
Set Timeout timeout

Sets the timeout used for waiting output in the current connection.

Read operations that expect some output to appear (Read Until, Read Until Regexp, Read Until Prompt, Login) use this timeout and fail if the expected output does not appear before this timeout expires.

The timeout must be given in time string format. The old timeout is returned and can be used to restore the timeout later.

Example:

${old} = Set Timeout 2 minute 30 seconds
Do Something
Set Timeout ${old}

See Configuration section for more information about global and connection specific configuration.
Switch Connection index_or_alias

Switches between active connections using an index or an alias.

Aliases can be given to Open Connection keyword which also always returns the connection index.

This keyword returns the index of previous active connection.

Example:

Open Connection myhost.net
Login john secret
Write some command
Open Connection yourhost.com 2nd conn
Login root password
Write another cmd
${old index}= Switch Connection 1 # index
Write something
Switch Connection 2nd conn # alias
Write whatever
Switch Connection ${old index} # back to original
[Teardown] Close All Connections

The example above expects that there were no other open connections when opening the first one, because it used index 1 when switching to the connection later. If you are not sure about that, you can store the index into a variable as shown below.

${index} = Open Connection myhost.net
Do Something
Switch Connection ${index}
Write text, loglevel=None

Writes the given text plus a newline into the connection.

The newline character sequence to use can be configured both globally and per connection basis. The default value is CRLF.

This keyword consumes the written text, until the added newline, from the output and logs and returns it. The given text itself must not contain newlines. Use Write Bare instead if either of these features causes a problem.

Note: This keyword does not return the possible output of the executed command. To get the output, one of the Read ... keywords must be used. See Writing and reading section for more details.

See Logging section for more information about log levels.
Write Bare text

Writes the given text, and nothing else, into the connection.

This keyword does not append a newline nor consume the written text. Use Write if these features are needed.
Write Control Character character

Writes the given control character into the connection.

The control character is prepended with an IAC (interpret as command) character.

The following control character names are supported: BRK, IP, AO, AYT, EC, EL, NOP. Additionally, you can use arbitrary numbers to send any control character.

Example:

Write Control Character BRK # Send Break command
Write Control Character 241 # Send No operation command
Write Until Expected Output text, expected, timeout, retry_interval, loglevel=None

Writes the given text repeatedly, until expected appears in the output.

text is written without appending a newline and it is consumed from the output before trying to find expected. If expected does not appear in the output within timeout, this keyword fails.

retry_interval defines the time to wait expected to appear before writing the text again. Consuming the written text is subject to the normal configured timeout.

Both timeout and retry_interval must be given in time string format. See Logging section for more information about log levels.

Example:

Write Until Expected Output ps -ef| grep myprocess\r\n myprocess
... 5 s 0.5 s

The above example writes command ps -ef | grep myprocess\r\n until myprocess appears in the output. The command is written every 0.5 seconds and the keyword fails if myprocess does not appear in the output in 5 seconds.