Linux – Bash scripting: Crossplatform check is python package installed in the system

bashlinuxunix

For example I want to check does py-sqlite3 available..? One of the methods would to call that command with some minimum python script and catch error?

I want to make check for any linux distro and unix system (at least bsd)

What could be the best way to achieve this?

P.s. Please provide example of shell scripting error catching, because I'm not so advanced in shell scripting

Best Answer

I have found existing answers incomplete and lacking good enough examples. Here is the solution I have settled on:

# an example checking if the pandas package is installed
if python -c 'import pkgutil; exit(not pkgutil.find_loader("pandas"))'; then
    echo 'pandas found'
else
    echo 'pandas not found'
fi

A Github gist of this example can be found here: https://gist.github.com/shaypal5/d505af9953cd86f59c750fa600ee4ba6

Related Solutions

Best Way to Check if a Volume is Mounted in a Bash Script – Linux Bash

Avoid using /etc/mtab because it may be inconsistent.

Avoid piping mount because it needn't be that complicated.

Simply:

if grep -qs '/mnt/foo ' /proc/mounts; then
    echo "It's mounted."
else
    echo "It's not mounted."
fi

(The space after the /mnt/foo is to avoid matching e.g. /mnt/foo-bar.)

Difference Between Double and Single Square Brackets in Bash – Scripting Shell POSIX

There are several differences. In my opinion, a few of the most important are:

[ is a builtin in Bash and many other modern shells. The builtin [ is similar to test with the additional requirement of a closing ]. The builtins [ and test imitate the functionality /bin/[ and /bin/test along with their limitations so that scripts would be backwards compatible. The original executables still exist mostly for POSIX compliance and backwards compatibility. Running the command type [ in Bash indicates that [ is interpreted as a builtin by default. (Note: which [ only looks for executables on the PATH and is equivalent to type -P [. You can execute type --help for details)
[[ is not as compatible, it won't necessarily work with whatever /bin/sh points to. So [[ is the more modern Bash / Zsh / Ksh option.
Because [[ is built into the shell and does not have legacy requirements, you don't need to worry about word splitting based on the IFS variable to mess up on variables that evaluate to a string with spaces. Therefore, you don't really need to put the variable in double quotes.

For the most part, the rest is just some nicer syntax. To see more differences, I recommend this link to an FAQ answer: What is the difference between test, [ and [[ ?. In fact, if you are serious about bash scripting, I recommend reading the entire wiki, including the FAQ, Pitfalls, and Guide. The test section from the guide section explains these differences as well, and why the author(s) think [[ is a better choice if you don't need to worry about being as portable. The main reasons are:

You don't have to worry about quoting the left-hand side of the test so that it actually gets read as a variable.
You don't have to escape less than and greater than < > with backslashes in order for them not to get evaluated as input redirection, which can really mess some stuff up by overwriting files. This again goes back to [[ being a builtin. If [ (test) is an external program the shell would have to make an exception in the way it evaluates < and > only if /bin/test is being called, which wouldn't really make sense.

Best Answer

Related Solutions

Best Way to Check if a Volume is Mounted in a Bash Script – Linux Bash

Difference Between Double and Single Square Brackets in Bash – Scripting Shell POSIX

Related Topic