xargs will concatenate many lines of its input and pass then to the specified command. For example:
echo -e 'line 1\nline 2\nline 3' | xargs echo
line 1 line 2 line 3
Since the arguments are sent to a single echo command (within the limits of the command line length).
Sometimes you want to use replacement string to put the arguments somewhere else in the command, rather than the end:
echo -e 'line 1\nline 2\nline 3' | xargs -Ix echo x DONE line 1 DONE line 2 DONE line 3 DONE
Now, xargs only substituted one argument per each echo invocation, because as the man page says "-I implies -L 1...". That's probably the right behavior for a typical case, but is there any way to override it, so I get
line 1 line 2 line 3 DONE as the output?
Please note that my example is illustrative only - I'm not very interested in non-xargs ways of tacking this issue.