Here's a simplified example of a script I'm writing (doesn't work as is).
I want to direct STDOUT from my script to the STDIN of a subprocess.
In the example below I'm writing 'test' to STDOUT and want that to get to the subprocess which ultimately writes it to the file output.
#!/bin/bash exec 4<&1 ( cat >/tmp/output )& <&4 while true; do echo test; sleep 1; done A (semi) standard technique for this sort of thing is:
#!/bin/sh test -t 1 && { $0 ${1+"$@"} | cat > /tmp/output; exit; } ... If the script is run with stdout on a tty, it is re-run with output piped to the cat.
In bash, you can use process substitution to create the subprocess and exec to redirect the script's output:
#!/bin/bash exec > >( cat >/tmp/output ) while true; do echo test; sleep 1; done 
The example is bizarre. Do you want the echo test stdout to be appended to /tmp/output? If so,
while true do echo test >> /tmp/output sleep 1 done The ultimate solution, thanks to @jon's pointer to coproc:
#!/bin/bash coproc CPO { cat >/tmp/output; } while true; do echo test >&${CPO[1]}; sleep 1; done In reality 'echo test' is replaced with a complex sequence of monitoring and parsing of a file, and the cat subprocess is replaced with a netcat to a server and that connection is monitored with a trap on the netcat process exiting.
Thanks for all the great answers!
echo testto be directed to the STDIN of another process, don't you?