Bug in the Bash Reference Manual

[John Lange]

In section "6.3.2 Is this Shell Interactive?", the Bash Manual advocates:

if [ -z "$PS1" ]; then
  echo This shell is not interactive
fi

however, this does not work in any shell I've tested (RedHat 4 & 5,  
OpenSUSE 11.1, SLES 10 & 11). It seems that the idea of testing the  
prompt variable was taken from section 5.5 of the (now) historical  
Unix F.A.Q. originally written in 1992.

In current Bash implementations, the "PS" variables are not set when  
invoking bash scripts interactively (I believe they are only set for  
login shells). Try this mini-script:

---
#!/bin/bash
set | grep PS
---

Even without the "#!/bin/bash", it still returns the same result.

However, "man bash" has a different idea, the "-t fd" test as in:

if [[ -t 0 ]] ; then
  echo interactive
fi

Good except that interactive scripts aren't always attached to a  
terminal. Sometimes they are attached to a socket. So:

if [[ -t 0 || -S /dev/stdin ]] ; then
  echo interactive
fi

Of course, just because stdin in bound to a socket doesn't prove that  
it's interactive since you could invoke it remotely with cron but  
presumably the author of the script would be aware of it's intended use.

Regards,
--
John Lange


----------------------------------------------------------------
This message was sent using IMP, the Internet Messaging Program.