Unless you coincidentally have a variable already call $session that coincidentally contains '$session', then you need to prevent the interpolation of the '$' that is being caused by use of 'qq', simply placing a '\' in front will achieve this.

Alternatively, as there is no real need for the interpolation in this case you could simple use 'q' instead of 'qq'

Example 1

my $sql = qq {
    select SID,SERIAL,USERNAME,STATUS,SCHEMANAME,OSUSER,
    PROCESS,MACHINE,TERMINAL,PROGRAM,TYPE,MODULE,
    to_char(LOGON_TIME,'DD-MON-YY HH24:MI:SS')"LOGON_TIME",
    STATE,SERVICE_NAME from v\$session order by LOGON_TIME DESC};
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Example 2

my $sql = q {
    select SID,SERIAL,USERNAME,STATUS,SCHEMANAME,OSUSER,
    PROCESS,MACHINE,TERMINAL,PROGRAM,TYPE,MODULE,
    to_char(LOGON_TIME,'DD-MON-YY HH24:MI:SS')"LOGON_TIME",
    STATE,SERVICE_NAME from v$session order by LOGON_TIME DESC};
[download]