Using shell script store PostgreSQL query on a variable - postgresql

Question

I want to store following postgreSQL query result in a variable. I am writing command on the shell script.
psql -p $port -c "select pg_relation_size ('tableName')" postgres
I need variable to save the result on a file. I have tried following but it is not working
var= 'psql -p $port -c "select pg_relation_size ('tableName')" '

Answer 1

Use a shell HERE document like:
#!/bin/sh
COUNT=`psql -A -t -q -U username mydb << THE_END
SELECT count (DISTINCT topic_id) AS the_count
FROM react
THE_END`
echo COUNT=${COUNT}
The whole psql <<the_end ... stuff here ... the_end statement is packed into backticks
the output of the execution of the statement inside the backticks is used as a value for the COUNT shell variable
The -A -t -q are needed to suppress column headers and error output
inside a here document, shell variable substitution works, even in single quotes!
So, you could even do:
#!/bin/sh
DB_NAME="my_db"
USR_NAME="my_name"
TBL_NAME="my_table"
COL_NAME="my_column"
COUNT=`psql -A -t -q -U ${USR_NAME} ${DB_NAME} << THE_END
SELECT COUNT(DISTINCT ${COL_NAME} ) AS the_count
FROM ${TBL_NAME}
THE_END`
echo COUNT=${COUNT}

Answer 2

to run a query inline you have to wrap it in grave accents, not single quotes:
$ vim `which fancyexecfileinpath`
psql lets you run queries from command line, but I guess you should be inputting complete information. you might be missing the database name.
postgres#slovenia:~$ psql -d mydbname -c "select * from applications_application;"
postgres#slovenia:~$ specialvar=`psql -d flango -c "select * from applications_application;"`
postgres#slovenia:~$ echo $specialvar
id | name | entities | folder | def_lang_id | ... | 2013-07-09 15:16:57.33656+02 | /img/app3.png (1 row)
postgres#slovenia:~$
notice the grave accents when assigning it to specialvar
otherwise you'll be setting it to a string.
There shouldn't be any space between the variable and the equals sign ("=") and the value ( http://genepath.med.harvard.edu/mw/Bash:HOW_TO:_Set_an_environment_variable_in_the_bash_shell )