#RUN: %fish %s function outnerr command echo out $argv command echo err $argv 1>&2 end outnerr 0 &| count #CHECK: 2 set -l tmpdir (mktemp -d) outnerr overwrite &> $tmpdir/file.txt cat $tmpdir/file.txt #CHECK: out overwrite #CHECK: err overwrite outnerr append &>> $tmpdir/file.txt cat $tmpdir/file.txt #CHECK: out overwrite #CHECK: err overwrite #CHECK: out append #CHECK: err append echo noclobber &>>? $tmpdir/file.txt #CHECKERR: {{.*}} The file {{.*}} already exists eval "echo foo |& false" #CHECKERR: {{.*}} |& is not valid. In fish, use &| to pipe both stdout and stderr. #CHECKERR: echo foo |& false #CHECKERR: ^ rm -Rf $tmpdir