using grep to find the value of a string

Question

I have file(file.txt) contains the following

aa=testing
bb=hello
cc=hi

Expected result

the value of aa is testing

How to use grep to find the value of aa?

grep aa= file.txt, but if you want the output to literally be the value of aa is testing , you can't use grep. — nos
– nos, Commented Aug 15, 2014 at 7:55

enrico.bacis · Accepted Answer · 2014-08-15 07:59:30Z

1

Use a positive lookbehind in grep:

grep -Po "(?<=aa=).*" file.txt

Output

testing

answered Aug 15, 2014 at 7:59

enrico.bacis

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Comments

Cyrus · Accepted Answer · 2014-08-15 09:16:16Z

1

grep -oP 'aa=\K.*' file.txt

Output:

testing

answered Aug 15, 2014 at 9:16

Cyrus

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konsolebox · Accepted Answer · 2014-08-15 07:56:30Z

0

awk -F= '/^aa=/ { print $2 }' file
sed -n '/^aa=/s|^.*=||p' file
sed -n 's|^aa=||p' file

Output:

testing

answered Aug 15, 2014 at 7:56

konsolebox

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Some golfing on the awk and you get awk -F= '/^aa/ && $0=$2'