xsel’s default behaviour depends on whether its input or output is connected to a terminal, so redirecting to and from files typically does the right thing. As mentioned by codeforester, the solution in your case is to run
xsel -b > file You can make your intent explicit by adding -o (when outputting the contents of the clipboard) or -i (when inputting to the clipboard). Without these options, if xsel’s context is indeterminate (i.e. neither standard input or standard output are connected to a terminal), it behaves in -o mode: xsel -b < /dev/null > file works as you’d expect, but xsel -b < file > /dev/null doesn’t.
You can also use xclip to copy the clipboard’s contents to a file:
xclip -sel c -o > file xclip can additionally request specific versions of the clipboard’s contents (known as targets), depending on the selection’s owner; for example, if you copied text from a web browser, you could retrieve it as HTML using
xclip -sel -c -o -t text/html > file The special TARGETS target will list the available targets:
xclip -sel -c -o -t TARGETS