Print R package function index to console

Question

I want to print the documentation for an R package to the console. Doing

utils:::.getHelpFile(help("print"))

works just fine but when I try

utils:::.getHelpFile(help(package="MASS"))

I get an error stating:

Error in dirname(file) : a character vector argument expected

So my question is: how can I print the documentation for an R package (i.e help(package="package_name")) to the console? Thanks in advance.

Answer 1

help(package = "MASS") takes you to the INDEX file for the MASS package, opened in a browser window (depending on your settings). To read that file into the console, we can use system.file() to get the file path, then readLines() to read it as a character vector.

## get the complete file path for the index file of the MASS package
f <- system.file("INDEX", package = "MASS")
## read it
readLines(f)
# [1] "Functions:"                                  
# [2] "========="
# [3] ""
# [4] "Null                    Null Spaces of Matrices"
# [5] "addterm                 Try All One-Term Additions to a Model"
# [6] "anova.negbin            Likelihood Ratio Tests for Negative Binomial GLMs"
# ...
# ...

Or we can wrap it in cat() to get a cleaner version

cat(readLines(f), sep = "\n")
# Functions:
# =========
#
# Null                    Null Spaces of Matrices
# addterm                 Try All One-Term Additions to a Model
# anova.negbin            Likelihood Ratio Tests for Negative Binomial GLMs
# ...
# ...

Alternatively, you could get the same result with

readLines(file.path(find.package("MASS"), "INDEX"))

Finally, if you're wondering about the links to the package description and news that appear at the top of the html browser, those can be obtained with

packageDescription("MASS")
news(package = "MASS")

Answer 2

utils:::.getHelpFile(help(package="MASS")) doesn't work because help(pacakge="MASS") returns a packageInfo class object, not a help_files_with_topic class object (which is a full file path with some other attributes).

Here's the simplest thing I can come up with:

cat(paste(format(help(package="MASS", help_type="text")), collapse="\n"),"\n")

Basically, you format the output from help(package="MASS"). Then paste that result into a single character string, collapsed together by newlines. Then call cat on that result.