Why does the comparison always return true when comparing two strings in bash?

Question

bash

Friends, hello everyone!

I’ll write right away that I’m not strong in writing bash scripts, but such a need arose.

I am attaching a simple example:

# !/bin/sh
res=$(curl -Isk https://........./api/rest.php | head -n 1 | sed 's/\r//g')
res_string="HTTP/1.1 200 OK"
if [ "$res"="$res_string" ]
then
service nginx status && service httpd status
else
echo "CANSEL"
fi

The problem is that when executed, the check always returns true, even if the check string is changed.
I broke my head, but I just can not understand the reason for this behavior.

Tell me where to dig.

UPD:
When testing with bash -x I get the following output:

bash -x script.sh 
++ curl -Isk https://...../api/rest.php
++ head -n 1
++ sed 's/\r//g'
+ res='HTTP/1.1 200 OK'
+ res_string='HTTP/1.1 200 OK'
+ '[' 'HTTP/1.1 200 OK=HTTP/1.1 200 OK' ']'
+ service nginx status
nginx (pid  17277) is running...
+ service httpd status
httpd (pid  17321) is running...

If res_string is changed to any value, then it will still be true.
For clarity:

bash -x script.sh 
++ curl -Isk https://......./api/rest.php
++ head -n 1
++ sed 's/\r//g'
+ res='HTTP/1.1 200 OK'
+ res_string='38942983478239423олвыалодлаывдHTTP/1.1 200 OK'
+ '[' 'HTTP/1.1 200 OK=38942983478239423олвыалодлаывдHTTP/1.1 200 OK' ']'
+ service nginx status
nginx (pid  17277) is running...
+ service httpd status
httpd (pid  17321) is running...

Answer 1

because there [ "$res" = "$res_string" ]are spaces between the space
The space is not put only when assigning a value to a variable
For example,res=123

Answer 2

#!/bin/sh
res=$(curl -lsk -o /dev/ev/null -w "%{http_code}" https://........./api/rest.php)
if [ "$res" = "200" ]; then
  service nginx status && service httpd status
else
  echo "CANCEL"
fi