How can we pass different browser at once in robotframework

I see 2 ways to do it.

1) loop over your browser and call a keyword that do your test:

*** Variables ***
@{BROWSERS}          firefox  chrome  IE

*** test cases ***
test with several browser
    :FOR  ${browser}  IN   @{BROWSERS}
    \  log to console  call keyword that does your test with ${browser}

Here is what you get with this test:

[Mac]$ pybot .
Browser.Ts
==============================================================================
test with several browser                                             
call keyword that does your test with firefox
call keyword that does your test with chrome
call keyword that does your test with IE
test with several browser                                             | PASS |
------------------------------------------------------------------------------
Browser.Ts                                                            | PASS |
1 critical test, 1 passed, 0 failed
1 test total, 1 passed, 0 failed
==============================================================================

2) another way (which I prefer) is to keep your ${BROWSER} variable with a single value and call your test case several time with a new value for the variable that you give on the command line:

[Mac]$ pybot --variable BROWSER:firefox ts.txt
[Mac]$ pybot --variable BROWSER:chrome ts.txt
[Mac]$ pybot --variable BROWSER:ie ts.txt