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I am new to bash. I have experience in java and python but no experience in bash so I'm struggling with the simplest of tasks.

What I want to achieve is I want to look through the string and find certain sub strings, numbers to be exact. But not all numbers just number that are followed by " xyz". For example:

string="Blah blah boom boom 14 xyz foo bar 12 foo boom 55 XyZ hue hue 15 xyzlkj 45hh."

And I want to find numbers: 14 55 and 15

How would I go about that?

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2 Answers 2

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You can use grep with lookahead

echo "$string" | grep -i -P -o '[0-9]+(?= xyz)'

Explanation:

  • -i – ignore case
  • -P – interpret pattern as a Perl regular expression
  • -o – print only matching
  • [0-9]+(?= xyz) – match one or more numbers followed by xyz

For more information see:

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4 Comments

I will take this one because it is explained better and provides some additional references. Thank you good sir.
Hi, i just have a follow up question. I want to add those numbers up and just print out the sum but I'm not sure how to do that. I tried: $result=expr $result + ${"$line" | grep -i -P -o '[0-9]+(?= xyz)'} and I get a ${"$line" | grep -i -P -o '[0-9]+(?= lešnik)'}: bad substitution
Hi, first declare result sum – declare -i sum, then foreach results and add each result to sum – for num in $(echo "$string" | grep -i -P -o '[0-9]+(?= xyz)'); do sum+=$num; done
That did it for me tyvm.
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grep + cut approach (without PCRE):

echo $string | grep -io '[0-9]* xyz' | cut -d ' ' -f1

The output:

14
55
15
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