Shell Programming and Scripting

$ awk -F'[][,="]' -v qq='"' -f remo.awk testlogs.txt
16/Oct/2012:13:12:55,E432834, Invalid credentials ,ag-agsos123-myss-dev2
15/Oct/2012:10:56:48,e420839,Invalid password format,ag-agsosg84-wid2-dev1
18/Oct/2012:04:49:25,shayne, Invalid credentials ,ag-wwsosg02-csj-dev1
11/Feb/2011:03:42:21,p468126, Invalid credentials - null password ,ag-wwsosg02-ds-dev1
11/Feb/2011:10:20:18,p457653, Invalid credentials ,ag-wwsosg02-rds-dev1
11/Feb/2011:10:09:09,p105666, Invalid credentials ,ag-agsos123-myss-dev2
07/Feb/2011:17:47:26,e420858, Invalid credentials ,ag-wwsosg02-rds-dev1

BEGIN {
  OFS=","
}
NF>=5{
  reason=$(NF-5)
  if (reason ~ /^[0-9][0-9]*/)
     reason=$(NF-4)

  match($0, "[^" qq "]* GET")
  agent=substr($0,RSTART, RLENGTH-4)

  print substr($2,1,index($2," ")-1),$5, reason,agent
}