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I want to replace exact word by sed command with variable. My file looks like this:

//module xyz
module xyz

Suppose I have the following shell variables defined:

var1='module xyz'
var2='module abc'

I want to change xyz to abc in uncommented line only(module xyz)

So after executing command output should be 

//module xyz    
module abc

I do not want to change commented line (//module xyz)

currently I am using sed command as,

sed -i "s|$var1|$var2|g" file_name

But this command doesn't work. It also replace commented line. How can I only replace the line that isn't commented?

Tom Fenech
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user5689562
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3 Answers3

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Assuming that you know the pattern is at the start of the line, you can use this:

sed "s|^$var1|$var2|" file_name

That is, add an anchor ^, so that the match has to be at the start of the line.

I removed the -i switch so you can test it and also the g modifier, which isn't necessary as you only want to do one substitution per line.

It's worth mentioning that using shell variables in sed is actually quite tricky to do in a reliable way, so you should take this into account.

Community
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Tom Fenech
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  • Your shell variable assignment should be quoted if there is space. Like:

    var1="foo bar blah"

  • You can add pattern, "the lines don't start with // " to your sed command, so that do your substitution only for those lines

This line should work for your example:

sed -i "\@^//@\!s/$var1/$var2/g" file
  • the ! needs to be escaped, because we used double quote
  • since your pattern (comment) has slash (/), I used other char as regex separator
  • This command will only do substitution on lines not starting with //. If there are leading spaces, you may want to adjust the pattern ^//
Kent
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0

You need to identify a pattern so that lines containing that pattern should not be processed. Assuming that // will exist only in commented lines you can use

sed -i '/\/\// !s/$var1/$var2/g' file_name

/\/\// will enable sed to identify lines which contain the pattern //, and !s will enable you to skip those lines.

Pintu
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