BASH: How to extract substring that is surrounded by specific text

Question

I am trying to extract numbers from file names that follow a specific pattern:

file-8923489_something.txt
another_file-8923489_something.txt
some-other_file-8923         


        

Answer 1

With grep:

$ echo "file-8923489_something.txt
another_file-8923489_something.txt
some-other_file-8923489_something.txt" | grep -Po '(?<=file-)\d+'
8923489
8923489
8923489

Or with pure bash:

d="your_string"
d1=${d%_*}
your_final_string=${d1##*-}

Test

$ d="file-8923489_something.txt"
$ d1=${d%_*}
$ echo $d1
file-8923489
$ echo ${d1##*-}
8923489

$ d="some-other_file-8923489_something.txt"
$ d1=${d%_*}
$ echo $d1
some-other_file-8923489
$ echo ${d1##*-}
8923489

$ d="another_file-8923489_something.txt"
$ d1=${d%_*}
$ echo $d1
another_file-8923489
$ echo ${d1##*-}
8923489