Sstrhsrtj

How to use sed regex to replace to words related to each other and one character between them with out change the character and the two words as group
like that

ahmed#mohamed 

ahmed$mohamed

ahmed7mohamed

I didn't want to replace ahmed only and then replace mohamed only

I used

sed -i 's/ahmed.mohamed/mohamed.ahmed/g'

but make all like this I want to keep the character between them.

mohamed.ahmed

mohamed.ahmed

mohamed.ahmed

You're very close. You need to use capturing parentheses:

sed -E -i 's/ahmed(.)mohamed/mohamed1ahmed/g'

The 1 is replaced with the text of the first set of parentheses.

You want to swap the two strings ahmed and mohamed that are separated by some character.

The issue in your expression,

s/ahmed.mohamed/mohamed.ahmed/

is that the character in-between the words is always replaced by a dot. The solution is to capture the character and replace it with itself.

This is one way of doing so with sed, which also uses the same capturing mechanism to avoid typing in the two strings again for the replacement:

sed 's/(ahmed)(.)(mohamed)/321/'

or,

sed -E 's/(ahmed)(.)(mohamed)/321/'

Testing on the given data:

$ sed -E 's/(ahmed)(.)(mohamed)/321/' <file

mohamed#ahmed

mohamed$ahmed

mohamed7ahmed