You seem to be referring to a non-current README (maybe you stumbled on that link via a web search?). Here are the current instructions from CRAN:
https://cran.r-project.org/web/packages/devtools/readme/README.html
Updating to the latest version of devtools
You can track (and contribute to) the development of devtools at https://github.com/hadley/devtools. To install it:
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Install the release version of devtools from CRAN with install.packages("devtools").
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Make sure you have a working development environment.
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Windows: Install Rtools.
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Mac: Install Xcode from the Mac App Store.
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Linux: Install a compiler and various development libraries (details vary across different flavors of Linux).
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Install the development version of devtools.
devtools::install_github("hadley/devtools")
Here is the devtools CRAN page:
https://cran.r-project.org/package=devtools
And the devtools github page:
But! Note that devtools has recently moved to the r-lib Github Organization, so the github links in the CRAN README are actually out of date. The latest instructions from the development version README:
Updating to the latest version of devtools
You can track (and contribute to) the development of devtools at https://github.com/r-lib/devtools. To install it:
-
Install the release version of devtools from CRAN with install.packages("devtools").
-
Install the development version of devtools.
devtools::install_github("r-lib/devtools")