Help related to clearing of shell scripting doubt

Shell Programming and Scripting
1

Hello Gurus,

Can anybody please help me to understand as what does this lines(Marked in bold) does:

_TABLESPACE_OFFLINE=`cat ${_tmp_res} | grep -iv "online" | grep -v "^[ ]*$" | grep -iv "SQL>"` ------->1

    if [ "X$\{\_TABLESPACE_OFFLINE\}" != "X" ];then
            \_tmp\_tablespace_status=1
            if\_need\_raise_alarm

Output of _TABLESPACE_OFFLINE from line 1 is:

TABLESPACE_NAME STATUS
------------------------------ ---------
EMA_PROCLOG_20120918 READ ONLY
EMA_PROCLOG_20120919 READ ONLY
EMA_PROCLOG_20120920 READ ONLY
TABLESPACE_NAME STATUS
------------------------------ ---------
EMA_PROCLOG_20120921 READ ONLY
EMA_PROCLOG_20120922 READ ONLY
EMA_PROCLOG_20120923 READ ONLY
EMA_PROCLOG_20120924 READ ONLY
EMA_PROCLOG_20120925 READ ONLY
EMA_PROCLOG_20120926 READ ONLY
EMA_PROCLOG_20120927 READ ONLY
20 rows selected.

2

It is actually checking whether the variabe _TABLESPACE_OFFLINE is empty or not.