Is there a way to use shell variables in a MongoDB query?
I have this for example:
#!/usr/bin/env bash
mongo --eval "use cdt_db; db.users.update({username:'${USER}'}, {'\$set':{roles:['Admin']}});"
I tried single quotes and double quotes, I get this error:
MongoDB shell version v3.4.9
connecting to: mongodb://127.0.0.1:27017
MongoDB server version: 3.4.9
2017-10-09T13:53:51.747-0700 E QUERY [thread1] SyntaxError: missing ; before statement @(shell eval):1:4
From the shell standpoint, your query is fine. Variable USER is expanded properly and $ in $set is properly escaped to prevent the shell parameter expansion.
The problem is in your use <dbname> part of the query. According to the docs:
You cannot use any shell helper (e.g.
use <dbname>,show dbs, etc.) inside the JavaScript file because they are not valid JavaScript.
Instead, you can use a JavaScript equivalent:
db = db.getSiblingDB('<dbname>')
or, better yet, specify the name of the database via command line argument:
mongo dbname --eval 'query'
Fixed, your query looks like:
mongo cdt_db --eval "db.users.update({username:'${USER}'}, {\$set:{roles:['Admin']}});"
For convenience (less escaping), you might sometimes also consider using single quotes, and concatenate the expanded variables (under double quotes):
mongo cdt_db --eval 'db.users.update({username:"'"${USER}"'"}, {$set:{roles:["Admin"]}});'
$setbe without the quotes? The safest way would be to write the expression under single quotes, concatenating it with variable values:mongo cdt_db --eval 'db.users.update({username:"'"$USER"'"}, {$set:{roles:["Admin"]}});'.mongo cdt_db --eval 'db.users.update({username:"'${USER}'"}, {$set:{roles:["Admin"]}});'$USERundergoes a shell parameter expansion (always, unless single-quoted). So ifUSER='*', then"$USER"will expand to*. However, if you don't double-quote it then it also goes through a pathname expansion (globbing), so$USERwill expand tofile1 file2 .... If you writecmd 'str' $USER, the variable is pathname-expanded (cmdreceivesstr file1 file2 ...), but if you writecmd 'str'$USER, then the variable is not pathname-expanded (unless has spaces), but spaces inUSERare not preserved! So the safe thing is to writecmd 'str'"$USER".