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edotan
Asked: 2012-04-19 01:29:11 +0800 CST

use sed in shell script to replace IP Address in a file

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I have a script that finds a string in a file replaces it with a new string.

$ sed -i 's/$old_string'/'$new_string'/g' $FILENAME

Now I need the condition to be a regular expression that also check whether the old string is followed with anything but a number.

I tried this but it didn't work:

$ sed -i -r 's/$old_string(^[0-9])+/$new_string/g' $FILENAME

Any idea?

linux centos shell sed regular-expressions

1 Answers

  1. Best Answer

    To negate a range in a regular expression, the caret must be inside the square brackets.

    sed -i -r 's/$old_string([^0-9])+/$new_string/g' $FILENAME

    The parentheses are also unnecessary in this case if you are not using backreferences (and it doesn't look like you are.)

    sed -i -r 's/$old_string[^0-9]+/$new_string/g' $FILENAME

    One last thing: bash doesn't parse variables inside single-quotes, so $old_string and $new_string will not be replaced by any bash variable you may have set in your script but will be used literally in that sed command. If you use double-quotes, they will be replaced.

    sed -i -r "s/$old_string[^0-9]+/$new_string/g" $FILENAME

    Update:

    Since the file doesn't contain anything after the string you want to replace, the [^0-9]+ part of the regex has nothing to match. It would work if there was a space after the IP address. We can match the end of the line instead with $.

    sed -i -r 's/123.123.123.1$/4.4.4.4/g' $FILENAME

    One more update. This one matches any character that isn't a number or no characters at all. For this one we need the parentheses to group the two options.

    sed -i -r 's/123.123.123.1([^0-9]+|$)/4.4.4.4/g' $FILENAME

    Since we have the parentheses, you can use a backreference to include whatever was matched:

    sed -i -r 's/123.123.123.1([^0-9]+|$)/4.4.4.4\1/g' $FILENAME
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