how to select
`pid number`
in
`users:(("postgres",pid=1644,fd=3))`
and pipe then to next command in terminal?

@Acer
echo -e "users:(("postgres",pid=1644,fd=3))" | grep -oP '(?<=pid=).*(?=,)'

@hakerdefo

Thanks I ll try to learn the options and the expression

Follow

@hakerdefo

-o
only

-P
perl-regexp

grep -options PATTERNS

PATTERNS

'......'
I didn't find definitions about this.

(...)
Grouping with Parentheses

(?=pattern)
is a positive look-ahead assertion

(?<=pattern)
is a positive look-behind assertion

I have one I cannot understand
what's the difference between
PATTERNS
and
'PATTERNS'

@Acer
Whenever you use a grep regular expression at the command prompt, surround it with quotes, or escape metacharacters (such as & ! . * $ ? and \) with a backslash (\).

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