how to use hostname variable in single quoted?

Question

In the bash file named "input_data"

LA=$1
curl -H 'Content-Type: application/x-ndjson' -XPOST '"'$LA'":9200/human_flow/human_flow/_bulk?pretty' --data-binary @$2.json

When running command

 ./input_data localhost human_flow

give error message

bash-3.2$ ./input_data localhost human_flow
curl: (6) Could not resolve host: "localhost"

localhost can be resolved

bash-3.2$ ping localhost
PING localhost (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=64 time=0.067 ms
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.156 ms

use 127.0.0.1 instead of localhost

bash-3.2$ ./input_data 127.0.0.1 human_flow
curl: (6) Could not resolve host: "127.0.0.1"

I mean it's pretty obvious it can't resolve `"localhost"`. Why do you have embedded double quotes surrounding it? — 123, Jun 03 '17 at 22:26
curl -H 'Content-Type: application/x-ndjson' -XPOST '$LA:9200/human_flow/human_flow/_bulk?pretty' --data-binary @$2.json also error — Chen Yu, Jun 03 '17 at 22:38
That's correct, it is. Why do you think you need to use single quotes, either to make your double-quotes literal or otherwise? — Charles Duffy, Jun 03 '17 at 22:38
To be clear, you *should* be using double-quotes -- if you just leave out quotes entirely it'll look like it works but be buggy. See http://shellcheck.net/ — Charles Duffy, Jun 03 '17 at 22:40

score 1 · Accepted Answer · answered Jun 03 '17 at 22:41

Correct usage would look like:

curl \
  -H 'Content-Type: application/x-ndjson' \
  -XPOST \
  --data-binary "@$2.json" \
  "$LA:9200/human_flow/human_flow/_bulk?pretty"

All expansions are in double quotes -- neither in single quotes (which prevents them from being expanded) nor unquoted.
Double quotes must not be inside single quotes if they are expected to have semantic meaning.
By POSIX convention, positional arguments should be specified after all optional arguments. Applications following GNU conventions don't strictly require this, but following it across-the-board avoids surprises.

how to use hostname variable in single quoted?

1 Answers1