Shell Programming and Scripting

I have a bunch of random character lines like ABCEDFG. I want to find all lines with "A" and then change any "E" to "X" in the same line. ALL lines with "A" will have an "X" somewhere in it. I have tried sed awk and vi editor. I get close, not quite there. I know someone has already solved this one.

Would this work?

Code:

 sed -e '/A/s/E/X/g'

Using awk

Code:

echo "ABCEDFG" | awk '/A/ {gsub("E","X")}1'
ABCXDFG

Is "A" always at the begin of line? Then try:

Code:

sed 's/^\(A[^E]*\)E/\1X/' file

ALL of the samples you gave me work fine. Many thanks.
I am working with a 500,000 record file, about 18meg, and the commands which work just fine on a small file are hanging on the large one. One has been "running" for two days. I have tried this on both SUN Solaris, and AIX flavors of Unix. Can anyone suggest something? Below are the commands I use. Again, they work just fine on the small test files I have used. It could be the size, or there could be something unique about the data in the larger file. Please help.
I have tried:

Code:

cat sun-file1.xml     | sed -e '/DESCRIPTION=/s/"/@@@"/g' > sun-file2.xml $

and

Code:

sed -e '/DESCRIPTION=/s/"/@@@"/g' <sun-file1.xml >sun-file2.xml

Pleas use code tags as required by forum rules!

Anchoring - if possible - sometimes really speeds things up, as the regex doesn't need to be searched in the whole line but in certain places. So, if "DESCRIPTION" always shows up in a constant position, count that relative to the BOL and use "^" in your regex.

EDIT: And, I guess, it scans lines twice: one for the address (/DESCRITPTION/), and then again for the occurrences of /"/. Maybe you can improve that:

Code:

sed 's/\(DESCRPITION[^"]*\)"/\1@@@"/' file

?

Sorry about the code tags. Now I understand and will use them in the future.
The first "find" is necessary. I only want to make the change in lines which contain the first "find" field. Once I find a line with "A" I want to change "E" to "X" in the same line. No way to change that (that I know of).
And there is some variation in where the "A" field is found.
I have it working fine in my simple short test file, but the long file it seems to hang on something. Very frustrating, so close and yet so far.