Perl: lookahead operators

Source: negative regex for perl string pattern match

(?=) - Positive look ahead assertion foo(?=bar) matches foo when followed by bar
(?!) - Negative look ahead assertion foo(?!bar) matches foo when not followed by bar
(?<=) - Positive look behind assertion (?<=foo)bar matches bar when preceded by foo
(?<!) - Negative look behind assertion (?<!foo)bar matches bar when NOT preceded by foo
(?>) - Once-only subpatterns (?>\d+)bar Performance enhancing when bar not present
(?(x)) - Conditional subpatterns
(?(3)foo|fu)bar - Matches foo if 3rd subpattern has matched, fu if not
(?#) - Comment (?# Pattern does x y or z)

Linux: top ten biggest files

du -a /var | sort -n -r | head -n 10

PostgreSQL: exclusive lock on a table

Source: Exploring Query Locks in Postgres

1 2 3 4 5

crmmbqt=# begin; lock table radius_db.radacct in access exclusive mode; BEGIN Time: 0.516 ms LOCK TABLE Time: 1001.108 ms

Then

1 2 3

crmmbqt=# rollback; ROLLBACK Time: 0.714 ms

PostgreSQL: list biggest tables

1	select table_schema||'.'||table_name as table, pg_size_pretty(size) as size from (select table_schema, table_name, pg_total_relation_size(table_schema||'.'||table_name) as size from information_schema.tables order by 3 desc) as foo;

PostgreSQL: dump and restore a table

Dump table:

pg_dump --table offer_db.dt_pool_ip -FC crmmbqt > /tmp/dt_pool_ip.sql

Restore table:

pg_restore --dbname crmmbqt --table=offer_db.dt_pool_ip dt_pool_ip.sql