how to control a shell script loop with: 'dpkg -s pv | grep Status'

Question

coding virgin needs help please - once package pv is installed this code doing always does else rather than then. Why?

# First check if pv package is installed, if not, install it first
PACKAGESTATUS=`dpkg -s pv | grep Status`;

if [[ $PACKAGESTATUS == S* ]]
   then
      echo "Package 'pv' is installed."
   else
      echo "Package 'pv' is NOT installed."
      echo "Installing package 'pv'. Please wait..."
      apt-get -y install pv
fi

nb it is part of a backup script that backs up a raspberry pi running Raspbian wheezy raspbian/2013-02-09 and pv is version 1.2.0 and the author is unavailable.

Thanks.

OK so `if [[ $PACKAGESTATUS == S* ]]` will be true just if `$PACKAGESTATUS` starts with `S` — fedorqui, Mar 22 '13 at 11:46
See http://stackoverflow.com/questions/1298066/check-if-a-package-is-installed-and-then-install-it-if-its-not — John Zwinck, Mar 22 '13 at 12:00
Yes I suspected that AND it doesn't work either. Thx for the link - solution works well — user1613312, Mar 22 '13 at 14:04

score 1 · Accepted Answer · answered Mar 22 '13 at 12:48

Instead of capturing the output of the dpkg | grep pipeline, just check its exit status:

if dpkg -s pv | grep -q Status; then
   then
      echo "Package 'pv' is installed."
   else
      echo "Package 'pv' is NOT installed."
      echo "Installing package 'pv'. Please wait..."
      apt-get -y install pv
fi

The -q option to grep is used to suppress the output of any matched lines, since you don't need to see them.

score 1 · Answer 2 · answered Sep 04 '13 at 20:41

There is a minor syntax error in chepners answer, due to the double 'then'.

I had better luck with this version

if `dpkg -s pv | grep -q Status;`
   then
      echo "Package 'pv' is installed."
   else
      echo "Package 'pv' is NOT installed."
      echo "Installing package 'pv'. Please wait..."
      apt-get -y install pv
fi

how to control a shell script loop with: 'dpkg -s pv | grep Status'

2 Answers2