Why does `ls | xargs wc -l` format prettily? Running `wc -l` (line count) individually on a file gives: λ wc -l pacman_Qemq.txt 235 pacman_Qemq.txt But running `ls | xargs wc -l` gives: λ ls | xargs wc -l 242409 pacman_database.tar.bz2 235 pacman_Qemq.txt 235 pacman_Qem.txt 807 pacman_Qeq.txt 807 pacman_Qe.txt 376 pacman_Qmq.txt 2276 pacman_Qnq.txt 2276 pacman_Qn.txt 2652 pacman_Qq.txt 2652 pacman_Qsq.txt 2652 pacman_Q.txt 257377 total How can this be? Why did the `total` show up? Why are the entries aligned? Shouldn't `xargs` be running `wc -l` individually on each file? Interestingly, `wc -l *` produces the same result.

By default, `xargs` will pass as many parameters on a single command line as it can - usually up to the shell limit of (IIRC) 256 characters. So the command you're using, `ls | xargs wc -l`, is functionally equal to `wc -l *`. The behavior I believe you're expecting is for `xargs` to run `wc` once for each file, which can be produced by adding the `-n` option, `ls | xargs -n 1 wc -l`.