5 Send URL: Opening a Web Browser

See also browser/external, which requires racket/gui, but can prompt the user for a browser if no browser preference is set.

On Windows, send-url normally uses shell-execute to launch a browser. (If the URL appears to contain a fragment, it may use an intermediate redirecting file due to a bug in IE7.)

On Mac OS X, send-url runs osascript to start the user’s chosen browser.

On Unix, send-url uses a user-preference, or when none is set, it will look for a known browser. See the description of external-browser for details.

If escape? is true, then str is escaped (by UTF-8 encoding followed by “%” encoding) to avoid dangerous shell characters: single quotes, double quotes, backquotes, dollar signs, backslashes, non-ASCII characters, and non-graphic characters. Note that escaping does not affect already-encoded characters in str.

On all platforms, external-browser parameter can be set to a procedure to override the above behavior — the procedure will be called with the url string.

The path, fragment, and query arguments are all encoded in the same way as a path provided to send-url, which means that already-encoded characters are used as-is.

When send-url/content is called, it scans old generated files (this happens randomly, not on every call) and removes them to avoid cluttering the temporary directory. If the #:delete-at argument is a number, then the temporary file is more eagerly removed after the specified number of seconds; the deletion happens in a thread, so if Racket exits earlier, the deletion will not happen. If the #:delete-at argument is #f, no eager deletion happens, but old temporary files are still deleted as described above.

On Unix, the command that is used depends on the 'external-browser preference. If the preference is unset, send-url uses the first of the browsers from unix-browser-list for which the executable is found. Otherwise, the preference should hold a symbol indicating a known browser (from the unix-browser-list), or it a pair of a prefix and a suffix string that are concatenated around the url string to make up a shell command to run. In addition, the external-browser paremeter can be set to one of these values, and send-url will use it instead of the preference value.

Note that the URL is encoded to make it work inside shell double-quotes: URLs can still hold characters like #, ?, and &, so if the external-browser is set to a pair of prefix/suffix strings, they should use double quotes around the url.

If the preferred or default browser can’t be launched, send-url fails. See get-preference and put-preferences for details on setting preferences.