[TUHS] What was your "Aha, Unix!" moment?

[William Corcoran]

You could cheat a little:

CHDIR=/usr/newFolder
echo “cd ${CHDIR}” > ./changeEnv
.   ./changeEnv


Bill Corcoran 


> On Oct 21, 2019, at 6:52 AM, "jason-tuhs at shalott.net" <jason-tuhs at shalott.net> wrote:
> 
> 
>>> % pwd
>>> /usr/ken
>>> % cd /tmp
>>> % pwd
>>> /usr/ken
>>> 
>>> Aha!
> 
>> I'm old and slow, had to think about that one.  Aha indeed!
> 
> I've actually been asking this (or, as a variation, how a child can set environment in its parent) as an interview question for unix sysadmins for the past fifteen or so years.  Maybe one in three gets it.
> 
> The answer that I'm secretly hoping for, no one has ever yet given me:
> 
> 
> hashbrown/home/jason-112719: /bin/pwd
> /home/jason
> 
> hashbrown/home/jason-112720: ./cd.sh /tmp
> 
> hashbrown/home/jason-112721: /bin/pwd
> /tmp
> 
> hashbrown/home/jason-112722: cat cd.sh
> cat: cd.sh: No such file or directory
> 
> hashbrown/home/jason-112723: cat ~/cd.sh
> #!/bin/sh
> 
> test -n "$1" && TARGET=$1 || TARGET=$HOME
> 
> ( echo "call (int) chdir(\"$TARGET\")" ; echo detach ; echo quit ) | gdb -q -p $PPID >/dev/null 2>&1 &
> 
> 
> "With ptrace(2) all things are possible."
> 
> 
> -Jason
>