CODEWITHSUNDEEP
regexsedgrepwildcardstring-substitution
Steve
Steve

Reputation: 12393

sed wildcard substitution

I want to do a substitution based on a wildcard. For example, change all "tenure" to "disposition" only if the word "tenure" comes after an '=' sign. Basically a regex that would match this =.*tenure

The sed command that I have so for this is:

sed 's/=.*tenure/=.*disposition/g' file.txt

However, if I pass this to a file containing:

blah blah blah = change "tenure" to "disposition"

I get 

blah blah blah =.*disposition" to "disposition"

instead of:

blah blah blah = change "disposition" to "disposition"

How do I do the substitution such that the wildcard in the regex won't be part of the destination file?

Upvotes: 6

Views: 23110

Answers (4)

MGwynne
MGwynne

Reputation: 3522

You need to use a capturing group to capture the text that appears between your equals sign and "tenure".

So

sed 's/=\(.*\)tenure/=\1disposition/g'

Note the use of \1 to reference and use the group you captured.

So in 

echo 'blah blah blah = change "tenure" to "disposition"' | sed 's/=\(.*\)tenure/=\1disposition/g'

we get

blah blah blah = change "disposition" to "disposition".

See Regex grouping.

Upvotes: 10

anubhava
anubhava

Reputation: 785531

You have to use backreference in sed. Use it like this:

sed 's/\(=.*\)tenure/\1disposition/g'

Upvotes: 2

Diego Sevilla
Diego Sevilla

Reputation: 29021

You need to save matched characters between the = and the tenure to add them to the output:

sed 's/=(.*)tenure/=\1disposition/g' file.txt

Also, you should add the -i option to sed if you want to edit the file inplace (do the modifications to the file itself).

Upvotes: 2

Seth Robertson
Seth Robertson

Reputation: 31461

sed 's/\(=.*\)tenure/\1disposition/g' file.txt

Upvotes: 2

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