How to check dependency in bash script - linux

Question

I want to check whether nodejs is installed on the system or not. I am getting this error:
Error : command not found.
How can i fix it?
#!/bin/bash
if [ nodejs -v ]; then
echo "nodejs found"
else
echo "nodejs not found"
fi

Answer 1

You can use the command bash builtin:
if command -v nodejs >/dev/null 2>&1 ; then
echo "nodejs found"
echo "version: $(nodejs -v)"
else
echo "nodejs not found"
fi

Answer 2

The name of the command is node, not nodejs
which returns the path to the command to stdout, if it exists
if [ $(which node 2>/dev/null) ]; then
echo "nodejs found"
else
echo "nodejs not found"
fi

Answer 3

This is not what the OP asked for (nearly 3 years ago!), but for anyone who wants to check multiple dependencies:
#!/bin/bash
echo -n "Checking dependencies... "
for name in youtube-dl yad ffmpeg
do
[[ $(which $name 2>/dev/null) ]] || { echo -en "\n$name needs to be installed. Use 'sudo apt-get install $name'";deps=1; }
done
[[ $deps -ne 1 ]] && echo "OK" || { echo -en "\nInstall the above and rerun this script\n";exit 1; }
Here's how it works. First, we print a line saying that we are checking dependencies. The second line starts a "for name in..." loop, in which we put the dependencies we want to check, in this example we will check for youtube-dl, yad and ffmpeg. The loop commences (with "do") and the next line checks for the existence of each command using the bash command "which." If the dependency is already installed, no action is taken and we skip to the next command in the loop. If it does need to be installed, a message is printed and a variable "deps" is set to 1 (deps = dependencies) and then we continue to the next command to check. After all the commands are checked, the final line checks to see if any dependencies are required by checking the deps variable. If it is not set, it appends "OK" to the line where it originally said "Checking dependencies.... " and continues (assuming this is the first part of a script). If it is set, it prints a message asking to install the dependencies and to rerun the script. It then exits the script.
The echo commands look complicated but they are necessary to give a clean output on the terminal. Here is a screenshot showing that the dependencies are not met on the first run, but they are on the second.
PS If you save this as an script, you will need to be in the same directory as the script and type ./{name_of_your_script} and it will need to be executable.

Answer 4

You may check the existence of a program or function by
type nodejs &>/dev/null || echo "node js not installed"
However, there is a more sophisticated explanation available here.

Answer 5

I was thinking about this and came up with a few versions, then went on the internet to see what others have to say and ended up here. Albeit an old thread, I'll reply with my thoughts.
First to answer the OP's original question: How can i fix it?
if node -v &>/dev/null; then
echo "nodejs found"
else
echo "nodejs not found"
fi
If you are simply checking if node works, this would do it. But it isn't a very generic way to do it.
Another way is to use command in a loop and collect the missing dependencies (in this example looking for the commands kind and kubectl).
for app in kind kubectl; do command -v "${app}" &>/dev/null || not_available+=("${app}"); done
(( ${#not_available[#]} > 0 )) && echo "Please install missing dependencies: ${not_available[*]}" 1>&2 && exit 1
Or less concisely expressed:
unset not_available # script safety, however not necessary.
for app in kind kubectl; do
if ! command -v "${app}" &>/dev/null; then
not_available+=("${app}")
fi
done
if (( ${#not_available[#]} > 0 )); then
echo "Please install missing dependencies: ${not_available[#]}" 1>&2
exit 1
fi
Then I figured I'd want a way to do the same without a loop, so came up with this:
not_installed=$(command -V kind kubectl 2>&1 | awk -F': +' '$NF == "not found" {printf "%s ", $(NF-1)}')
[[ -n ${not_installed} ]] && echo "Please install missing dependencies: ${not_installed}" 1>&2 && exit 1
The command -V can take any number of entries and posts the result back to stdout and stderr (though I redirect both to stdout for the next command to parse).
awk sets the field separator to <colon><one or more space>, expressed as : +. If the last field contains, "not found", print the second to last field, being the name of the command which is not installed.
Lastly, if the variable contains any data, then report back which dependencies that are missing to stderr and exit the script!
You can do dependency checks in a million ways, but here are a few alternatives which are more generally applicable and not too lengthy while still being easy to follow. :]

Answer 6

If all you want is to check to see if a command exists, use which command. It returns the patch if the command is called, and nothing if it is not found
if [ "$(which openssl)" = "" ] ;then
echo "This script requires openssl, please resolve and try again."
exit 1
fi