How to extract a value from a string using regex and a shell

Question

I am in shell and I have this string  12 BBQ  45 rofl  89 lol  Using the regexp   d     rofl   I want 45 as a result   Is it correct to use regex to extract data from a string  The best I have done is to highlight the value in some of the online regex editor  Most of the time it remove the value from my string   I am investigating expr  but all I get is syntax errors   How can I manage to extract 45 in a shell script

User · Answer

Using ripgrep s replace option  it is possible to change the output to a capture group  rg --only-matching --replace   1     d   rofl    --only-matching or -o outputs only the part that matches instead of the whole line  --replace   1  or -r replaces the output by the first capture group

User · Answer

You can use rextract to extract using a regular expression and reformat the result   Example       echo  12 BBQ  45 rofl  89 lol      rextract        d    rofl     1   45

User · Answer

It seems that you are asking multiple things  To answer them    Yes  it is ok to extract data from a string using regular expressions  that s what they re there for You get errors  which one and what shell tool do you use  You can extract the numbers by catching them in capturing parentheses       d   rofl     and using  1 to get the string out     is for  the rest before and after on the same line    With sed as example  the idea becomes this to replace all strings in a file with only the matching number   sed -e  s     d   rofl    1 g  inputFileName  gt  outputFileName   or   echo  12 BBQ  45 rofl  89 lol    sed -e  s     d   rofl    1 g

User · Answer

You can certainly extract that part of a string and that s a great way to parse out data  Regular expression syntax varies a lot so you need to reference the help file for the regex you re using  You might try a regular expression like    0-9     a-zA-Z     0-9      a-zA-Z    0-9     a-zA-Z     If your regex program can do string replacement then replace the entire string with the result you want and you can easily use that result   You didn t mention if you re using bash or some other shell  That would help get better answers when asking for help

User · Answer

you can use the shell bash for example     string  12 BBQ  45 rofl  89 lol    echo   string  rofl   12 BBQ  45   string   string  rofl     echo   string      45

User · Answer

Yes regex can certainly be used to extract part of a string  Unfortunately different flavours of  nix and different tools use slightly different Regex variants   This sed command should work on most flavours  Tested on OS X and Redhat   echo  12 BBQ  45 rofl  89 lol    sed   s        0-9  0-9         1 g

User · Answer

You can do this with GNU grep s perl mode   echo  12 BBQ  45 rofl  89 lol  grep -P   d     rofl   -o   -P means Perl-style  and -o means match only

[regex] How to extract a value from a string using regex and a shell?

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