Crash on Mercurial book production

[Guido Ostkamp]

Hi,

the following article was originally sent to Bryan O' Sullivan, but as I 
got no response, I'm reposting it here, maybe someone else can help:

I am running into a problem with the production of the Mercurial book. All 
the code examples which contains a 'help' command cause a Mercurial crash.

I tried to investigate this a bit and found that in 
en/examples/run-example there is code that forks with pty.fork() before 
exec'ing some bash shell.

When Mercurial gets e.g. the 'hg help init' command, some mechanism gets 
involved which tries to split the lines accurately according to the number 
of columns of the terminal. This code uses Mercurial 'util.py' function 
termwidth().

By introducing some debug lines I figured that on my system the COLUMNS 
variable doesn't seem to be set any longer when the code is called through 
the 'run-example' sequence.

Mercurial then crashes as shown below.