If you want to process just the files under A/
, then a simple for
loop should be enough:
for file in A/*.dat; do ./a.out < "$file" > "${file%.dat}.ans"; done
Here's an example of how bad things may turn if you use ls
with xargs
for the job. Consider a following scenario:
- first, let's create some empty files:
touch A/mypreciousfile.dat\ with\ junk\ at\ the\ end.dat
touch A/mypreciousfile.dat
touch A/mypreciousfile.dat.ans
- see the files and that they contain nothing:
$ ls -1 A/
mypreciousfile.dat
mypreciousfile.dat with junk at the end.dat
mypreciousfile.dat.ans
cat A/*
- run a magic command using xargs:
ls A/*.dat | xargs -I file sh -c "echo TRICKED > file.ans"
- the result:
$ cat A/mypreciousfile.dat
# TRICKED with junk at the end.dat.ans
$ cat A/mypreciousfile.dat.ans
# TRICKED
So you've just managed to overwrite both mypreciousfile.dat
and mypreciousfile.dat.ans
. If there were any content in those files, it'd have been erased.
If you'd like to insist on using xargs
, use -0
(null-terminated names):
find A/ -name "*.dat" -type f -print0 | xargs -0 -I file sh -c './a.out < "file" > "file.ans"'
Notice two things:
- this way you'll create files with
.dat.ans
ending; - this will break if some file name contains a quote sign (
"
).
Both issues can be solved by different way of shell invocation:
find A/ -name "*.dat" -type f -print0 | xargs -0 -L 1 bash -c './a.out < "$0" > "${0%dat}ans"'
find A/ -name "*.dat" -type f -exec sh -c './a.out < "{}" > "{}.ans"' \;
This, again, produces .dat.ans
files and will break if file names contain "
. To go about that, use bash
and change the way it is invoked:
find A/ -name "*.dat" -type f -exec bash -c './a.out < "$0" > "${0%dat}ans"' {} \;