list output truncated - How to expand listed variables with str() in R

I have a data.frame df with 600+ variables. I'm writing a function that automates the creation of columns and need to visually check them once.

The str function provides a good summary:

str(df)
'data.frame':   29 obs. of  602 variables:
 $ uniqueSessionsIni: POSIXct, format: "2015-01-05 15:00:00" "2015-01-05 16:00:00" "2015-01-05 17:00:00" ...
 $ uniqueSessionsEnd: POSIXct, format: "2015-01-05 15:59:00" "2015-01-05 16:59:00" "2015-01-05 17:59:00" ...
 $ m0p0             : POSIXct, format: "2015-01-05 15:00:00" "2015-01-05 15:00:00" "2015-01-05 15:00:00" ...
 $ m1p0             : POSIXct, format: "2015-01-05 15:01:00" "2015-01-05 15:01:00" "2015-01-05 15:01:00" ...
 $ m2p0             : POSIXct, format: "2015-01-05 15:02:00" "2015-01-05 15:02:00" "2015-01-05 15:02:00" ...    

and it goes on...
but truncates the output, as below:

$ m33p1            : POSIXct, format: "2015-01-05 15:34:00" "2015-01-05 15:34:00" "2015-01-05 15:34:00" ...
$ m34p1            : POSIXct, format: "2015-01-05 15:35:00" "2015-01-05 15:35:00" "2015-01-05 15:35:00" ...
$ m35p1            : POSIXct, format: "2015-01-05 15:36:00" "2015-01-05 15:36:00" "2015-01-05 15:36:00" ...
$ m36p1            : POSIXct, format: "2015-01-05 15:37:00" "2015-01-05 15:37:00" "2015-01-05 15:37:00" ...
[list output truncated]

How can I display the full list of 602 variables?

You can use the argument list.len:

str(df, list.len=ncol(df))

and if you want to print more observations you could set the argument vec.len, also have a look at ?str for documentation of all arguments.