Using variable inside of sed -i (regex?) bash

Question

I've looked at the other sed pages here and i cannot find one that uses -i with a variable in the regex search portion. I am trying to cut out a requested line in the file myresolv.conf and by getting its line number. 5 people in my class are all stuck :( Any help is awesome

line=$(grep -n "$3" ./myresolv.conf | cut -d: -f1)

sed -i "$line"  ./myresolv.conf

possible duplicate of Remove a specific line from a file WITHOUT using sed or awk — tripleee
– tripleee, Commented Oct 8, 2013 at 16:31

twalberg · Accepted Answer · 2013-10-08 16:32:36Z

1

It would seem you want to delete a specific line from a file. You're hopefully getting a single line number in your line variable (but beware - if you have multiple lines that match, you're going to get a list of numbers, and that will cause the rest of your process to explode). The problem you have is that the command you are feeding sed is simply the line number - you are not specifying anything for sed to do with that line number. So, perhaps you want this:

sed -i "${line}d" file.txt

If I've misunderstood your question, and you're not wanting to delete that line, but simply print it, then replace the d with p...

answered Oct 8, 2013 at 16:32

twalberg

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2 Comments

Joel Damata Over a year ago

I want to delete the line but this isnt working for me, i get sed: -e expression #1, char 2: unknown command: ` '

twalberg Over a year ago

Perhaps your line variable contains something other than a number, then...? Or you have a version of sed that wants an argument to -i, like sed -i bak "3d" file.txt...

jkshah · Accepted Answer · 2013-10-08 17:52:42Z

1

I assume, you mean remove line when you say cut out line.

Try using grep with -v option. I believe you don't need sed here.

grep -v "$3" ./myresolv.conf

Or if you want to delete line in the file itself

sed -i.bak "/$3/d" ./myresolv.conf

It's good to use -i with .bak to create backup file before overwirting changes.

edited Oct 8, 2013 at 17:52

answered Oct 8, 2013 at 16:16

jkshah

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1 Comment

Kalpesh Panchal Over a year ago

Finally someone with an answer that really works. Thanks @jkshah

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