如何判断bash中是否安装了npm模块

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