Bash shell read error: 0: Resource temporarily unavailable

Question

When writing a bash script. Sometimes you are running a command which opens up another program such as npm, composer.. etc. But at the same time you need to use read

Answer 1

Usually it is important to know what input the invoked program expects and from where, so it is not a problem to redirect stdin from /dev/null for those that shouldn't be getting any.

Still, it is possible to do it for the shell itself and all invoked programs. Simply move stdin to another file descriptor and open /dev/null in its place. Like this:

exec 3<&0 0

The above duplicates stdin file descriptor (0) under file descriptor 3 and then opens /dev/null to replace it.

After this any invoked command attempting to read stdin will be reading from /dev/null. Programs that should read original stdin should have redirection from file descriptor 3. Like this:

read -r var 0<&3

The < redirection operator assumes destination file descriptor 0, if it is omitted, so the above two commands could be written as such:

exec 3<&0