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mattiav27
Asked: 2019-09-02 09:37:40 +0800 CST

How can I modify a line which contains 2nd occurence of a string?

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This post explains how to add a line at the beginning of a file from the terminal. But how do I modify from the terminal a line somewhere in a file if I do not know which line it is?

I should modify the line eni=10.*10**9 to eni=10.*10**8 note the exponents. It is the second time that eni appears

command-line

3 Answers

  1. Best Answer

    I think this is what you want:

    line=$(grep -n -m2 "eni" file | tail -n1 | cut -f1 -d:)

sed -i $line's/9$/8/' file
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  2. Since Ubuntu now ships with GNU Awk v4.0+ (which provides an inplace module) you could do something like

    gawk -i inplace '/eni=/ {if (++c == 2) sub(/10\*\*9/,"10**8")} 1' file

    You can make the regular expressions /eni=/ and/or /10\*\*9/ more or less specific as required.

    Similarly in perl

    perl -i -pe 'if (/eni=/) {s/10\*\*9/10\*\*8/ if (++$c == 2)}' file
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  3. Using sed:

    sed -i ': 1 ; N ; $!b1 ; s/eni\=10\.\*10\*\*9/eni\=10\.\*10\*\*8/2' filename

    / is one of the delimiters and \ is the escape character. \ is used so that bash won't interpret special characters as some command, like * as wildcard.

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