How to determine if npm module installed in bash

Question

My objective is to only install this npm package if it's not already available. This continues to to execute even when I've installed the module globally.

if [ npm list -g widdershins &> /dev/null ] || [ ! -d node_modules ]; then
    npm install widdershins --no-shrinkwrap
fi

How can I adjust this to detect when it's installed globally?

Answer 1

if you want a one liner:

Local

npm list | grep widdershins || npm install widdershins --no-shrinkwrap

Global:

npm list -g | grep widdershins || npm install -g widdershins --no-shrinkwrap

Answer 2

package='widdershins'
if [ `npm list -g | grep -c $package` -eq 0 ]; then
    npm install $package --no-shrinkwrap
fi

alternative including the directory check:

package='widdershins'
if [ `npm list -g | grep -c $package` -eq 0 -o ! -d node_module ]; then
    npm install $package --no-shrinkwrap
fi

Explaination:

• npm list -g lists all installed packages
• grep -c $package prints a count of lines containing $package (which is substituted to 'widdershins' in our case)
• -eq is an equals check, eg $a -eq $b returns true if $a is equal to $b, and false otherwise.
• -d checks if the given argument is a directory (returns true if it is)
• ! is the negation operator, in our case is negates the -d result
• -o is the logical or operator

To sum it up:

• First code: if the $package is installed, then the -eq result is false and this causes the if statement to be false. If $package is not installed, then the -eq result is true (and the if statement is also true).
• Second code: in addition to description of first code, if node_module is a directory, then the if statement is false. If node_module is not a directory then the if statement is true. And this is independend from the -eq result because of the logical or connection.

This could also help you.

Answer 3

This worked for me:

package_name='widdershins'
if [[ "$(npm list -g $package_name)" =~ "empty" ]]; then
    echo "Installing $package_name ..."
    npm install -g $package_name
else
    echo "$package_name is already installed"
fi

npm list -g package-name returns empty when is not installed, so with that condition you can check if it contains the string empty