CODEWITHSUNDEEP
sed
fluca1978
fluca1978

Reputation: 4058

sed property substitution

I've got a property file where I want to do a property substitution, so I wrote a sed patter to change

host = 1234

with another value, but when I execute

echo "host = 1234" | sed 's/\#*\(host[ \t]*\)\=\([ \t]\d*\)/\1\=\1/g'

I got that the substitution is done (host =host) but the \2 atom is also appended to the end of the string (1234). How can I remove it?

 `host =host 1234

Upvotes: 0

Views: 101

Answers (2)

sorpigal
sorpigal

Reputation: 26086

The first problem is that \d doesn't do what you think. Use [0-9] at least.

You still get host =host out, which seems crazy to me.

EDIT:

Okay

echo "host = 1234" | sed 's/#*\host[ \t]*=[ \t]*\([0-9]*\)/host = asdf/g'
  • Why capture 'host' if it's always the same? Just rewrite it.
  • Why preserve the exact tab/space information? Just rewrite it.
  • Why escape things which are not special?

I hope you get the idea.

But here's what you probably want:

sed '/^#/!s/[ \t]*\([^ \t]*\)[ \t]*=[ \t]*\([^ \t]*\)/\1 = newvalue/g' input_file

This will change anything = anything to anything = newvalue in non-commented lines of input_file. To make it a specific key which is replaced by newvalue, use:

sed '/^#/!s/[ \t]*\(host\)[ \t]*=[ \t]*\([^ \t]*\)/\1 = newvalue/g' input_file

to e.g. replace only lines reading host = anything.

Upvotes: 2

synthesizerpatel
synthesizerpatel

Reputation: 28036

Does this suit your needs?

echo "host = 1234" | cut -d"=" -f 1

yields

host

Then,

echo "host = 1234" | cut -d"=" -f 1

yields 

1234

Upvotes: 0

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