21 Oct
2019
21 Oct
'19
4:45 p.m.
> % 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