How to replace a string using Sed?

Question

Suppose I have a string like this

<start><a></a><a></a><a></a></start>

I want to replace values inside <start></start> like this

<start><ab></ab><ab></ab><ab></ab><more></more><vale></value></start>

How do I do this using Sed?

Answer 1

Try this :

sed 's@<start>.*</start>@<start><ab></ab><ab></ab><ab></ab></start>@' file

Answer 2

I get this line with gnu sed :

sed -r 's#(<start>)(.*)(</start>)#echo "\1"$(echo "\2"\|sed  "s:a>:ab>:g")"\3"#ge'  

see example:

kent$  echo "<start><a></a><a></a><a></a><foo></foo><bar></bar></start>"|sed -r 's#(<start>)(.*)(</start>)#echo "\1"$(echo "\2"\|sed  "s:a>:ab>:g")"\3"#ge'                 
<start><ab></ab><ab></ab><ab></ab><foo></foo><bar></bar></start>

note

this will replace the tags between <start>s which ending with a . which worked for your example. but if you have <aaa></aaa>:

you could do: (I break it into lines for better reading)

sed -r 's#(<start>)(.*)(</start>)
 #echo "\1"$(echo "\2"\|sed "s:<a>:<ab>:g;s:</a>:</ab>:g")"\3"
 #ge' 

e.g.

kent$  echo "<start><a></a><a></a><a></a><aaa></aaa><aba></aba></start>" \
 |sed -r 's#(<start>)(.*)(</start>)#echo "\1"$(echo "\2"\|sed  "s:<a>:<ab>:g;s:</a>:</ab>:g")"\3"#ge'
<start><ab></ab><ab></ab><ab></ab><aaa></aaa><aba></aba></start>

Answer 3

sed 's/(\<\/?)a\>/\1ab\>/g' yourfile, though that would get <a></a> that was outside <start> as well...

Answer 4

grep -rl 'abc' a.txt | xargs sed -i 's/abc/def/g'