Merge pull request #43 from kpedro88/fix_call_host_caveats

Fix call_host.sh caveats

Author: kpedro88

README.md

@@ -12,7 +12,7 @@ Table of Contents
    * [Details](#details)
    * [Options](#options)
    * [HTCondor jobs](#htcondor-jobs)
-   * [Caveats](#caveats)
+   * [Interactive commands and signals](#interactive-commands-and-signals)
 * [bind_condor.sh](#bind_condorsh)
    * [Usage](#usage-1)
    * [Setting up bindings](#setting-up-bindings)
@@ -171,14 +171,13 @@ or placed in a file `~/.callhostrc` (automatically detected and sourced by `call
     ```
 * Using the `ENV()` function in the JDL file may not function as intended, since it will be evaluated on the host node, rather than inside the container with your environment set up.
 
-### Caveats
+### Interactive commands and signals
 
-* Commands that require tty input (such as `nano` or `emacs -nw`) will not work with `call_host`.
-* Occasionally, if a command fails (especially when calling multiple commands separated by semicolons), the pipe will break and the terminal will appear to hang. The message "Interrupted system call" may be shown.
-    It is necessary to exit and reenter the container (in order to create a new pipe) if this occurs.
-    To prevent this, chain multiple commands using logical operators (`&&` or `||`), or surround all the commands in `()` (thereby running them in a subshell).
-* Stopping a command in progress with ctrl+C is disabled (to avoid breaking the pipe as described in the previous item).
-* Suspending a command with ctrl+Z is not supported and may break the session.
+* Commands that require tty input (such as `nano` or `emacs -nw`) now work with `call_host`, provided you are using `call_host` interactively (i.e. your terminal is a real tty). When both the input and output of `call_host` are a terminal, the host command is run under a pseudo-terminal (pty) so that full-screen and interactive programs behave normally.
+    * This requires `python3` on the host node (present on essentially all interactive nodes). If `python3` is unavailable, `script` is used as a fallback (interactive programs still work, but ctrl+C is delivered via the slower signal path described below); if neither is available, the command runs without a pty (as before).
+* Your stdin is forwarded to the host command, so piping or redirecting input works, e.g. `echo data | call_host some_command` or `call_host some_command < input.txt`.
+* Pressing ctrl+C now interrupts the running host command (and returns you to your prompt) instead of being ignored, in both interactive and non-interactive use. The container session is left intact.
+* Pressing ctrl+Z does not suspend the host command (job-control suspension cannot be supported across the container boundary), but it no longer breaks the session or leaves a stray process on the host: the keystroke is simply ignored and the command keeps running. Use ctrl+C if you want to stop it.
 
 ## `bind_condor.sh`