unlinkapps: avoid deleting too many symlinks

Use `start_with?` to make sure the symlink actually points into one of
the Homebrew directories (depending on given arguments). Previously,
only a substring match was used, which would also remove a symlink to a
hypothetical `/opt/unrelated/usr/local/opt/Unrelated.app`. Even if
unlikely to occur, altering stuff unrelated to Homebrew is bad.

Furthermore, make sure to always use a trailing slash with directories.
Otherwise, e.g., `brew unlinkapps qt` will unlink .app bundles of both
`qt` and `qt5` if both are installed and `brew linkapps qt qt5` was
issued before. (Please ignore that `qt` and `qt5` offer a conflicting
set of .app bundles. This will have to be addressed elsewhere.)

Closes Homebrew/homebrew#45174.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/Library/Homebrew/cmd/unlinkapps.rb b/Library/Homebrew/cmd/unlinkapps.rb
index 2674b2854..86db7a932 100644
--- a/Library/Homebrew/cmd/unlinkapps.rb
+++ b/Library/Homebrew/cmd/unlinkapps.rb
@@ -25,9 +25,9 @@ module Homebrew
 
   def should_unlink?(file)
     if ARGV.named.empty?
-      file.match(HOMEBREW_CELLAR) || file.match("#{HOMEBREW_PREFIX}/opt")
+      file.start_with?("#{HOMEBREW_CELLAR}/", "#{HOMEBREW_PREFIX}/opt/")
     else
-      ARGV.kegs.any? { |keg| file.match(keg.to_s) || file.match(keg.opt_record.to_s) }
+      ARGV.kegs.any? { |keg| file.start_with?("#{keg}/", "#{keg.opt_record}/") }
     end
   end
 end