How to keep restarting a Windows cmd prompt

Question

Cygwin's bash is often preferable to Windows' cmd command shell, so we use it to set up our environments before spawning a Windows shell. However, halting execution of a running process in this spawned shell with Ctrl-C kills boots the user back to the bash shell.

My attempted workaround:

source setupEnvironment.sh

restartCommand() {
  # Reset trap
  trap restartCommand SIGINT
  echo -e " === Restarting windows cmd prompt\n"
  cmd /k 
}

trap restartCommand SIGINT
echo -e " === Starting windows cmd prompt\n"
cmd /k

This approach only restarts cmd once. Subsequent Ctrl-C's are not caught. Is there a way to keep restarting the cmd process?

Curious why you can't do everything in bash itself, why do you need to start cmd at all? — Miserable Variable, Jan 30 '13 at 21:37
@Miserable Variable: personally, I'm happy staying in bash. But others at work want the cmd prompt. So I compromised: I'll invoke cmd, but only after setting up the environment in bash (bash does everything better!). — tcdaniel, Jan 30 '13 at 21:45

score 2 · Accepted Answer · answered Jan 30 '13 at 22:40

2

Does it have to be in the same window? If not, I have had much better luck with

cygstart cmd

cmd starts in its own window; and only exit closes that window

answered Jan 30 '13 at 22:40

Miserable Variable

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Nice workaround. The extra window isn't ideal, but everything then works as expected. – tcdaniel Jan 30 '13 at 23:32
The cygstart options `--wait` might be useful here. – Miserable Variable Jan 30 '13 at 23:50
I tried that - but the process stays on in the background without the user knowing. Just an extra process and a couple MB of RAM, but when you rarely restart your PC, that could add up. – tcdaniel Jan 31 '13 at 03:10
Which process? Bash? How is `bash` started? Another alternative is for the bash process to exit after starting cmd using cygstart (without --wait). BTW even when you start cmd without cygstart the bash process stays in memory – Miserable Variable Jan 31 '13 at 03:16
Whoops, my last comment referred to `--hide`. This closed the window but the parent **process** stayed active. Trying `--wait` didn't seem to do anything useful either. Yes, the best solution for now is `cygstart cmd /K; exit`. What I didn't say was this bash prompt was actually started from a cmd prompt - so the bash prompt is effectively sandwiched between 2 cmd prompts, unknown to the user. So exiting bash doesn't exit the original cmd prompt. – tcdaniel Jan 31 '13 at 03:21
Oh hmmm. Given this scenario I think it is best if you set the environment in cmd itself :) Or perhaps create a .bat file using bash (change `export x=y` to `echo set x=y >> envvars.bat` and execute the generated bat file from cmd, where a called bat file can modify the caller's env – Miserable Variable Jan 31 '13 at 03:24
Haha - yeah, that's where I started, with 2 parallel scripts to setup a development environment (on Linux and Windows). There is significant overlap, so I combined them to reduce maintenance. Thanks for the help. – tcdaniel Jan 31 '13 at 03:36

score 1 · Answer 2 · answered Jan 30 '13 at 21:32

1

Subsequent Ctrl-Cs aren't caught because your script exits due to reaching the end.

Chances are cmd will return error when you ctrl-c, in which case you could do

until cmd /k; do true; done

Otherwise, make your script loop, until ctrl-c isn't pressed:

trap restart=1 SIGINT
echo -e " === Starting windows cmd prompt\n"
restart=1
while (( restart )); do restart=0; cmd /k; done

answered Jan 30 '13 at 21:32

that other guy

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Thanks - both answers works reasonably well, and may be the best I can hope for. When cmd is in the middle of compiling, Ctrl-C still frequently boots back to bash though. Also, the cmd window sometimes locks up and may be closed only by End Process from Task Manager. – tcdaniel Jan 30 '13 at 23:25

score 1 · Answer 3 · edited May 23 '17 at 12:09

To complement Miserable Variable's helpful answer with an explanation of why opening cmd.exe in its own console window is the best approach:

While you can try to work around the Ctrl-C issue as demonstrated in that other guy's answer, the behavior is not quite the same as in a regular cmd.exe console window: since a new instance of cmd.exe is created every time Ctrl-C is pressed, previous state is lost.
The Cygwin terminal (console window) uses the UTF-8 character encoding rather than the regular console window's encoding that is based on the (legacy) OEM code page, and the two are incompatible.
Curiously, staying in the Cygwin terminal causes cmd.exe to echo all interactively submitted commands (as you'd get in a batch file without @echo off).

To automatically close the Cygwin window when launching the cmd.exe console window, use
exec cygstart cmd.

How to keep restarting a Windows cmd prompt

3 Answers3