Shell Script mktemp, what’s the best method to create temporary named pipe?

I’m aware its best to create temporary files with mktemp, but what about named pipes?

I prefer things to be as POSIX compliant as possible, but Linux only is acceptable. Avoiding Bashisms is my only hard criteria, as I write in dash.

Answers:

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Method 1

tmppipe=$(mktemp -u)
mkfifo -m 600 "$tmppipe"

Unlike regular file creation, which is prone to being hijacked by an existing file or a symbolic link, the creation of a name pipe through mkfifo or the underlying function either creates a new file in the specified place or fails. Something like : >foo is unsafe because if the attacker can predict the output of mktemp then the attacker can create the target file for himself. But mkfifo foo would fail in such a scenario.

If you need full POSIX portability, mkfifo -m 600 /tmp/myfifo is safe against hijacking but prone to a denial of service; without access to a strong random file name generator, you would need to manage retry attempts.

If you don’t care for the subtle security problems around temporary files, you can follow a simple rule: create a private directory, and keep everything in there.

tmpdir=
cleanup () {
  trap - EXIT
  if [ -n "$tmpdir" ] ; then rm -rf "$tmpdir"; fi
  if [ -n "$1" ]; then trap - $1; kill -$1 $$; fi
}
tmpdir=$(mktemp -d)
trap 'cleanup' EXIT
trap 'cleanup HUP' HUP
trap 'cleanup TERM' TERM
trap 'cleanup INT' INT
mkfifo "$tmpdir/pipe"

Method 2

A safer alternative is to use mktemp to create a directory safely, then put your named pipe inside that directory, do an rm -R $dir to get rid of it in the end.

Method 3

Use the “dry-run” option:

mkfifo $(mktemp -ut pipe.XXX)

Method 4

You can use mktemp to create a temporary file, then delete it and create a named pipe with the same name.

For example:

TMPPIPE=$(mktemp -t pipe.XXX) && {
    rm -f $TMPPIPE
    mkfifo $TMPPIPE
}

Method 5

Use mkfifo or mknod in Unix, where by two separate processes can access the pipe by name — one process can open it as a reader, and the other as a writer.

mkfifo my_pipe
gzip -9 -c < my_pipe > out.gz
cat file > my_pipe

The named pipe can be deleted just like any file:

rm my_pipe

mkfifo --mode=0666 /tmp/namedPipe
gzip --stdout -d file.gz > /tmp/namedPipe

NamedPipe can be used a regular file for only reading once.

http://www.linuxjournal.com/article/2156

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0