which(1) prints error messages on stdout, breaking shell scripts and common usage patterns: ldd `which foo` ldd: foo:: No such file or directory ldd: Command: No such file or directory ldd: not: No such file or directory ldd: found.: No such file or directory X=$(which foo 2>/dev/null) test -n "$X" || echo "foo not found" This works contrary to the csh builtin it was modeled after and `which' from coreutils. The patch below fixes that. As a bonus, print "which: " in front of ...