ep_svr_<any number>_<3 letters>_<3 letters>_<any character>

How aboot

my @strs = qw(
  ep_svr_1_abc_ZYX_!
  ep_svr_2_DEF_wvu_?
  ep_svr_3_GhI_tSr_#
  ep_svr_x_aaa_bbb__
 xep_svr_2_ccc_ddd_x
  ep_svr_4_ee_ffff_y
);

for(@strs) {
  print m< ^ ep_svr_ \d _ [A-Za-z]{3} _ [A-Za-z]{3} _ . \z >xi ?
     "valid pattern: $_\n" : "invalid pattern: $_\n";
}

__output__

valid pattern: ep_svr_1_abc_ZYX_!
valid pattern: ep_svr_2_DEF_wvu_?
valid pattern: ep_svr_3_GhI_tSr_#
invalid pattern: ep_svr_x_aaa_bbb__
invalid pattern: xep_svr_2_ccc_ddd_x
invalid pattern: ep_svr_4_ee_ffff_y
[download]

There I'm using the /x modifier so whitespace doesn't effect the regex, non-standard delimiters (just personal preference) and \z to specify the end of the string (not the end of the line). See perlre and perlop for more info.
HTH

_________
broquaint