tr command - need to change string not characters 1

[AlbertAguirre]

I need to duplilcate the last line in a file but change certain elements.

For instance:
tail -1 filename.txt

produces:
123 abc 456 def 123

I need to change all instances of "123" to "99".

I tried this:
tail -1 filename.txt | tr "123" "99"

But the result is:
993 abc 456 def 993

This is because "tr" does a character to character conversion. I need it to change the entire "123" string.

I cannot find the answer in man tr.

Help?

 

[RodKnowlton]

sed is the better tool for this.

tail -1 filename.txt | sed 's/123/99/g'

Rod Knowlton
IBM Certified Advanced Technical Expert pSeries and AIX 5L
CompTIA Linux+
CompTIA Security+

 

[AlbertAguirre]

Thanx!

I used the ! instead of /