Shell Script – Piping Data to a Process’s stdin Without Causing EOF

pipeshell-scriptstdin

I have an executable that starts a user-interactive shell. I would like to, upon launch of the shell, inject a few commands first, then allow the user to have their interactive session. I can do this easily using echo:

echo "command 1\ncommand 2\ncommand3" | ./shell_executable

This almost works. The problem is that the echo command that is feeding the process's stdin hits EOF once it's done echoing my commands. This EOF causes the shell to terminate immediately (as if you'd pressed Ctrl+D in the shell).

Is there a way to inject these commands into stdin without causing an EOF afterwards?

Best Answer

Found this clever answer in a similar question at stackoverflow

(echo -e "cmd 1\ncmd 2" && cat) | ./shell_executable

This does the trick. cat will pump in the output of echo into input stream of shell_executable and wait for more inputs until EOF.

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Bash – Dump process’s stdin and stdout

The simplest approach would be to use tee to dump the input to and output from the child to two separate files like so:

#!/bin/bash
tee in.log | child | tee out.log

You could use tee's -a parameter (append) to write both logs to the same file, but I'm not quite sure if they'll be interleaved in the right order or just written one after the other:

#!/bin/bash
tee -a both.log | child | tee -a both.log

Shell – cat into stdin then pipe into program keeps forked shell open, why

For the cases where it "works", you are leaving a process running cat which is reading its standard input, which has not been closed. Since that is not (yet) closed, cat continues to run, leaving its standard output open, which is used by the shell (also not closed).

Best Answer

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Bash – Dump process’s stdin and stdout

Shell – cat into stdin then pipe into program keeps forked shell open, why

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