psql shell command execution with \!

Using `\!` with `\o`..

You can combine the two like this,

\! echo "SELECT 1;" > bar (runs the command echo "SELECT 1;" redirects output of SELECT 1; to bar)
\o bar (runs the commands in bar)

Seems to be impossible for \!,

but one can set a variable from external command output,

testdb=> \set content `cat my_file.txt`

and then using this var in sql expression like this:

testdb=> INSERT INTO my_table VALUES (:'content');

postgresql shell psql

You can use \o <filename> option to specify the output file or use COPY command to solve your problem.