help with a script

**Avidanborisov** · June 22nd, 2011

I need to implement in a larger script of mine, bash code that will check if some packages are installed, if yes, do something, if not do something else.
can someone give me an example code of how should I do it?

**gmargo** · June 22nd, 2011

You can use dpkg(1) to test for installed packages:

Code:

#!/bin/sh
pkglist="dpkg foobar"
for PKG in $pkglist
do
    dpkg -l $PKG >/dev/null 2>/dev/null
    if [ $? -eq 0 ]; then
        echo "Package $PKG is installed"
    else
        echo "Package $PKG is NOT installed"
    fi
done

Code:

$ ./pkgtest.sh 
Package dpkg is installed
Package foobar is NOT installed

**Avidanborisov** · June 23rd, 2011

Thank you! this is just what I needed!

**Avidanborisov** · June 25th, 2011

hey, just another quick question.
In the script I have a variable that contains a string with 4 letters.
How can I split it into to two variables, one that contains the first three letters and another that contains only the last letter?
edit: nevermind, I used offsets.

**nothingspecial** · June 25th, 2011

Code:

$ f="abcd"
$ g="${f:0:3}"
$ h="${f:3:1}"
$ echo "$g"
abc
$ echo "$h"
d

***Edit Oh you got it. cool

**gmargo** · June 25th, 2011

My mind automatically thought of using sed(1). Offsets are bash-specific and not part of the standard shell, so make sure you use the proper she-bang (#!/bin/bash).