pass variable from node to bash exec

Question

I am using this pattern to execute bash scripts:

const exec = util.promisify(require('child_process').exec);

async function myBash() {
    try {
        const { stdout, stderr } = await exec("echo hi");

        console.log(stdout);

    } catch (err){
       console.error(err);
    };
  };

How can I pass the variable greeting to the exec command - non working:

const exec = util.promisify(require('child_process').exec);
const greeting = "hello";

async function myBash(greeting) {
    try {
        const { stdout, stderr } = await exec("echo", greeting);

        console.log(stdout);

    } catch (err){
       console.error(err);
    };
  };

Sahil Thummar · Accepted Answer · 2022-02-01 03:06:36Z

2

const exec = require('child_process').exec;
const greeting = "hello";

async function myBash(greeting) {
  try {
    const {
      stdout,
      stderr
    } = await exec(`echo ${greeting}`);
    console.log(stdout);
  } catch (err) {
    console.error(err);
  };
};
myBash(greeting);

answered Feb 1, 2022 at 3:06

Sahil Thummar

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Amadan · Accepted Answer · 2022-02-01 02:25:55Z

exec will execute a command line (a string) by feeding it to a shell. You have two options:

Not great in this use-case: use exec with a string that incorporates arguments:
```
exec(`echo '${greeting}'`);
```
or equivalently
```
exec("echo '" + greeting + "'");
```
Note that this breaks down if the argument contains single quotes, so they need to be sanitised or properly escaped if you do not trust the arguments.
Much better in this case: use a function that is designed to pass arguments directly to an executable - execFile:
```
execFile("echo", [greeting]);
```
Note that this does not invoke shell; here it actually executes /bin/echo, not the bash builtin echo. It also does not parse any arguments, so wildcards, variables etc will not be substituted.

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