How to grep my one-line file with constant key?

Question

This is my file

__version__="1.11.10"

numerical part will change all the time and I want to grep this.

new_tag=`grep -Eo '[0-9]+\.[0-9]+\.[0-9]+'_version.py`

failed. how to extract 1.11.10 ?

Answer 1

You may use sed:

sed -n 's/.*="\([^"]*\)"/\1/p' file

To assign to a variable:

new_tag=$(sed -n 's/.*="\([^"]*\)"/\1/p' file)

See the online Bash demo.

Details

• -n - suppresses default line output in the sed command
• .*="\([^"]*\)" - a POSIX BRE pattern that matches
  • .* - any text then
  • =" - a =" string
  • \([^"]*\) - capturing group #1 that captures zero or more chars other than "
  • " - a " char
• \1 - replaces the match with Group 1 contents
• p - prints the resulting value