How to make a bash script to check if a program or library exists

Question

I want to make a function to check if the program or library is already installed.

Thats what I do now:

dpkg --status software-properties-common | grep -q not-installed
if [ $? -eq 0 ]; then
    sudo apt-get install -y software-properties-common
fi

What I want:

isPackageNotInstalled() {???} 

if [ $(isPackageNotInstalled 'software-properties-common') ]; then 
   sudo apt-get install -y software-properties-common
fi

any help would be greatly appreciated.

IMHO it's rarely a good idea to name functions with a negative. It's much easier to be sure what the return value means if you test if PackageXYZisInstalled. Obviously YMMV. — Mark Setchell
– Mark Setchell, Commented Aug 9, 2018 at 21:29

GAD3R · Accepted Answer · 2018-08-10 09:23:27Z

2

A sample script including a function to check and install the missing package:

#!/bin/bash

isPackageNotInstalled() {

    dpkg --status $1 &> /dev/null
    if [ $? -eq 0 ]; then
    echo "$1: Already installed"
    else
    sudo apt-get install -y $1
    fi
    }

isPackageNotInstalled $1

save it as script , usage ./script package_name.

man dpkg :

EXIT STATUS
       0      The requested action was successfully performed.  Or a check  or
              assertion command returned true.

       1      A check or assertion command returned false.

       2      Fatal  or unrecoverable error due to invalid command-line usage,
              or interactions  with  the  system,  such  as  accesses  to  the
              database, memory allocations, etc.

edited Aug 10, 2018 at 9:23

answered Aug 9, 2018 at 21:10

GAD3R

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Comments

Alan · Accepted Answer · 2018-08-09 18:02:15Z

1

I see that dpkg --status has several return values that can imply partially-installed or pending packages. My thought would be to use its return code rather than checking for any particular text. Full disclosure - I can't try this with actual dpkg right now, but something quick you can try....

So for a simple command:

if ! (dpkg --status "..." &>/dev/null); then ...

or more simply:

dpkg --status "..." &>/dev/null || sudo apt-get ...

and to put it in a function:

function isPackageNotInstalled() { ! dpkg --status "$1" &>/dev/null }

then to use it:

if isPackageNotInstalled "..."; then ...

or, as above, just:

isPackageNotInstalled "..." && sudo apt-get ...

Hope this helps.

answered Aug 9, 2018 at 18:02

Alan

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Comments

Tek aEvl · Accepted Answer · 2020-02-18 04:51:44Z

0

This script works in #archlinux also, based on the the answer already chosen.

isPackageNotInstalled() {

    pacman -Ss $1 &&> /dev/null
    if [ $? -eq 0 ]; then
    echo "$1: Already installed"
    else
    sudo pacman -S $1
    fi
    }

isPackageNotInstalled $1

for yaourt

isPackageNotInstalled() {

    yaourt -Ss $1 &&> /dev/null
    if [ $? -eq 0 ]; then
    echo "$1: Already installed"
    else
    yaourt -S $1
    fi
    }

isPackageNotInstalled $1

answered Feb 18, 2020 at 4:51

Tek aEvl

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