CODEWITHSUNDEEP
regexbashsed
Ryan
Ryan

Reputation: 2084

sed: match between quotes, first instance only

I've read several related posts, but I haven't got my sed string right yet. How can I find the first line that contains myVariable="something", and change what is between the quotation marks to some variable (this is in a shell script)?

I've tried:

sed -i '/myVariable/s/"\([^"]*\)"/"${1}"/' /file

But this inserted $1 into all instances of myVariable="".

If I put "0," before the command like I've seen other posts suggest, then it no longer matches on lines with "myVariable". Instead it replaces the first instance of quotes on every line.

Followup questions: will it make a difference if I want to match a variable with a space in it? What if I want to replace the nth instance of myVariable=""?

Example file.txt:

<blah myVariable="this" />
<blah myVariable="that" />
<blah myVariable="the other thing" />

if I pass in apple to:

sed -i '/myVariable/s/"\([^"]*\)"/"'"${1}"'"/' /file.txt

file.txt becomes:

<blah myVariable="apple" />
<blah myVariable="apple" />
<blah myVariable="apple" />

but I want:

<blah myVariable="apple" />
<blah myVariable="that" />
<blah myVariable="the other thing" />

edit 2:

I tried 

sed -i -e '0,/myVariable/s/"\([^"]*\)"/"${1}"/' /file

but that gave me something like:

<foo bar="${1}" />
<blah myVariable="${1}" />
<blah myVariable="${1}" />
<blah myVariable="${1}" />
<alpha bravo="${1}" charlie="notchanged"/>

Note: I don't care about the $1, that can be changed by escaping correctly. I'm more worried that instead of changing the first instance of myVariable, I've now changed the first instance of "" on every single line (regardless of myVariable).

Upvotes: 0

Views: 985

Answers (3)

tivn
tivn

Reputation: 1923

This is how we can do that with Perl:

perl -pe 'if (/(myVariable)="[^"]*"/) { s//$1="apple"/ if ++$i==1 }' -i a.txt

This will works whether or not there is whitespace inside the quote pair. For only the n-th regex match, replace 1 in ++$i==1 with n.

Upvotes: 1

Ed Morton
Ed Morton

Reputation: 204229

Just use awk:

$ awk -v new="apple" '!f && sub(/myVariable="[^"]+/,"myVariable=\""new){f=1} 1' file       
<blah myVariable="apple" />
<blah myVariable="that" />
<blah myVariable="the other thing" />

Upvotes: 2

RTLinuxSW
RTLinuxSW

Reputation: 842

Break in and out of single quotes

sed -i '/myVariable/s/"\([^"]*\)"/"'"${1}"'"/' /file

Upvotes: 0

Related Questions