Sunday, January 11, 2015

Looking through the window, the expect-lite debugger

Looking through the debugger
In January 2015, expect-lite will have been making automation easier for 10 years. In celebration of that event, version 4.8.0, includes improvements to the debugger to make automation even easier.

expect-lite has had an integrated debugger,  called with *INTERACT, since version 4.0 (Oct 2010).The expect-lite debugger allows you to:
  • all the standard debugger stuff: step, skip, view variables
  • type commands directly to the device/host the script is connected to
  • execute arbitrary lines of expect-lite script (copy/paste uses this as well)
The debugger has the standard things you would look for in a debugger. Pressing escape h will print the debugger help:

IDE: Help
  Key          Action
  ----        ------
  <esc>s      Step
  <esc>k      sKip next step
  <esc>c      Continue
  <esc>v      show Vars
  <esc>e      show Env
  <esc>0to9   Show N next lines of script
  <esc>-1to-9 Show N previous lines of script
  ctrl+D      Quit & Exit expect-lite
  <esc>h      this Help

The debugger is like a window to the device being automated. Once in a breakpoint, the debugger silently steps aside, and allows you to type directly to the device. Perhaps you aren't getting the response you expected, or the device wasn't configured as you had expected. You can fix it while in the middle of your script.

The debugger silently watches what you type, and decides if the text is for the device, or is it an expect-lite command it must execute. How does it do this? Mostly pretty well.

Typing expect-lite commands in the debugger

You may have noticed that expect-lite commands start with a punctuation character like '>', '<', '?', '@', or ';'. The debugger watches for these characters at the beginning of a line. But there are some tweaks to prevent the debugger from accidentally grabbing a line that was intended for the device. These are limitations only when typing in the debugger, and are not required when executing the expect-lite script.
  • >send this    There must be no space between > and the text to be sent
  • ; comment   There must be a space between the semi-colon and the comment
  • ?if condition...   When using an IF statement in the debugger then the optional 'if' must be used, there are just too many question marks in normal text
  • $var=value  Variable assignments must have an equals sign (no spaces)
  • no white space before the expect-lite command (punctuation)
I wrote in an earlier blog entry (writing scripts with copy and paste), that using the debugger you can also copy/paste into a running script. When copy/pasting into the debugger, only the first line need follow the above limitations, the remaining lines can have leading white space, etc, since the debugger has decided that the entire paste is expect-lite script.


The biggest improvement to the debugger in version 4.8.0,  is *SHOW ENV. Similar to *SHOW VARS, the expect-lite environment consists of a list of directives which are enabled/disabled, such as *INFO, and *TIMESTAMP, as well as ones with values like user defined prompt, and the infinite loop count (*INFINITELOOP). Lastly, *SHOW ENV will display any shell environment variables which begin with EL_.

$ DEBUG Info: Printing expect-lite directives/environment
Environment:          Value:
DEBUG                 off
DVPROMPT              on
EOLS                  LF
EXP_INFO              on
INFO                  on
LOG                   off
LOG_EXT               .log
NOFAIL                2
NOINCLUDE             off
NOINTERACT            off
REMOTE_SHELL          none
TIMESTAMP             off
WARN                  on
fuzzy_range           10
timeout               2
EL_REMOTE_HOST        localhost

Of course, if you are in the debugger, you don't have to type *SHOW ENV, you can just type <esc>e.

Just as you can start a new shell, by typing 'bash' or 'csh' at the prompt. There is an included example called 'el_shell.elt' which you can use to create an expect-lite shell. It is a simple script which just drops you into the debugger. From there, you can type regular linux commands (or cygwin linux-like commands), expect-lite commands, or explore the debugger help with <esc>h.

Doughnut Scripts

I find I often create a doughnut script, a script with a hole in the middle. I use this to have a script set up my environment, then drop to the debugger, allowing me to plunk around, then when I am done, I exit the debugger (with '+++'), and the script cleans up. I call this automation assist. It doesn't do everything, but it allows me to explore/test faster than doing it all by hand.

The debugger command detection isn't perfect, but it works pretty well. Sometimes you may find a smudge or a dirty spot on the debugger window, but hopefully, it will be clear enough to see that expect-lite is automation for the rest of us.