Mongoexport 尝试导出超过 120 天的条目，shell 变量不起作用

Question

I have made a shell script and I am trying to export entries older than 1 day from my db. My DB has a field named "problemDate" which contains dates in string format in yyyy-mm-dd format such as (2021-03-22)

mongoexport --host localhost --db pagesuccess --collection problem -q='{ "problemDate": { "$lte" : "2021-03-22"}} ' --type=csv --out text2.csv --fields date,problemDetails,problem,tags,url,language,institution,section,theme
  connected to: mongodb://localhost/
  exported 8 records
--------------------------------------------------------------------------------------------------------------------
older1Day=$(gdate --date="1 days ago" +%F)
mongoexport --host localhost --db pagesuccess --collection problem -q='{ "problemDate": { "$lte" : "$older1Day"}} ' --type=csv --out text2.csv --fields date,problemDetails,problem,tags,url,language,institution,section,theme
  connected to: mongodb://localhost/
  exported 0 records

I'm really not sure about why the second does not work but the first works. The only difference is I am using a variable for the date in the second command. I'm really curious as to why the second one does not work.

Answer 1

The variables won't be expanded without placing them in double as opposed to single quotes. The command therefore needs to be re-written as:

mongoexport --host localhost --db pagesuccess --collection problem -q="{ \"problemDate\": { \"$lte\" : \"$older1Day\"}}" --type=csv --out text2.csv --fields date,problemDetails,problem,tags,url,language,institution,section,theme

Answer 2

the problem was because I was using single quotes. In Bash you can't interpolate variables in single quotes like you can with double quotes.

This worked well:

older120Days=$(gdate --date="1 days ago" +%F)
mongoexport --host localhost --db pagesuccess --collection problem -q='{ "problemDate": { "$lte" : "'"$older120Days"'"}} ' --type=csv --out text2.csv --fields date,problemDetails,problem,tags,url,language,institution,section,theme