Shell Programming and Scripting

I need to search and replace a particular string in a file. Only the exact match of the string should be replaced.
eg: File contents : abc abcd abcdef
--> Replace only 'abc' with 'xyz', but it should not replace abcd with xyzd.

So the o/p should be: xyz abcd abcdef.

How can this be done? I tried sed 's/\<abc\>/xyz/g' , but it dint work.

Any help would be appreciated.

Thanks in advance!

Code:

echo "abc abcd abcdef" | sed -e 's/^abc/xyz/g'

I tried it. It dint work. Let me be more specific. The string need not be at the beginning of the line:

i/p: abcd abc abcdef
o/p: abcd xyz abcdef

Thanks!

Code:

echo "string" | sed -e 's/ abc / xyz /g' | sed -e 's/^abc /xyz /g' -e 's/ abc$/ xyz/g'

Hello i am not very sure how to do this using sed options , there could far better way though.
In the above code i just took care about
1. abc at starting of the string
2. abc at end of the string
3. abc in between the string

Your first example should work using the <> to define a "word" but only with GNU sed or GNU awk and similar enhanced SEDs and AWKs. There are SEDs and AWKs out there that have a not as broad understanding of regular expressions like the modern GNU versions.
On most Linux boxes your line should work flawless.

Afaik you will have to emulate the <word> RegExp behaviour like reddybs posted. Only thing I see is it could be written so sed is called only once, but I would go with that too, example:

Code:

$> echo "abc abcd abcde abc abcd xabc dabc"| sed '
> s/ abc / ooo /g
> s/^abc /ooo /g
> s/ abc$/ ooo/g
> '
ooo abcd abcde ooo abcd xabc dabc

Thanks zaxxon and reddybs. That worked!