#21 2017-08-27 07:05:26

johnraff

nullglob

From: Nagoya, Japan

Registered: 2015-09-09

Posts: 12,560

Website

Re: [SOLVED] Adding makemkv to openbox menu

bl-multimedia-pipemenu seems to run two checks to determine if a program is install.  The first place is to look for a /var/lib/dpkg/info/{package}.list file.  I think the second check is to look for the the same file in /etc (clarification on the grep -Evq line would be appreciated).  If either condition is satisfied, then the script "thinks" the package is installed.

You've almost got it. The basic test is to look for a /var/lib/dpkg/info/{package}.list file. This file is created whenever dpkg installs a package, and lists all the files installed on the system by that package. The complication is that after a package is removed - but not purged - then some conffiles are kept. As long as the conffiles remain, then so will the *.list file, even after the package is uninstalled. Luckily, except in a few rare cases, all the conffiles are under /etc. So the allInstalled() function does this:
1) If the file "/var/lib/dpkg/info/${package}.list" does not exist: The package is not installed.
2) If the file exists, but all the files in its list are under /etc: The package is not installed.
3) Otherwise: The package is installed.
(Rare false positives are given if the package has conffiles under /usr...)
(Please see 'man grep' for explanation of the options.)

The reliable way of testing if a package is installed is to ask dpkg directly with a test like this:

[[ $(dpkg-query --show --showformat='${db:Status-Abbrev;2}' "$package" 2>/dev/null) = ii ]] && echo "$package is installed."

But this is much slower. The pipemenu has to run that test on every item in the menu, and using the dpkg call makes it distinctly sluggish.

Anyway:

...a better way of detecting whether a package is installed or not: look for its command in $PATH.

The new pipemenus should get round that, and make the /var/lib/dpkg/info/${package}.list hack unnecessary.

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If you try to place "firefox" in the menus...

Of course, you would be expected to use the name of a package that actually exists!

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...elevator in the Brain Hotel, broken down but just as well...
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