Problem: Search and replace a with a.alt, then search and replace t with t.alt yields a few a.alt.alt artifacts. I'm not sure that, even if there is such a thing, a simultaneous search and replace function would prevent this outcome. However, if you replace all your as and ts with different characters--say, dagger and daggerdbl--a subsequent search of † and replace with a.alt would avert the problem...

You need to state what text editor you are using. There is no such thing as "GREP" :-) There is a sort of basic functionality, but details in semantics and supported functionality differs wildly among GREP-aware editors.

Using InDesign's GREP syntax, something like this ought to work: search for

\b([at])\b

and replace with

$1.alt

-- note this will only change the two examples you provided, and "at the same time" as well. Somehow I don't think there is any text editor that allows you to specify a host of strings to change at the same time ...

On the Mac, I use the line command sed. For instance, if the file test contains

ccommaaccent
gcommaaccent
kcommaaccent
scommaaccent
tcommaaccent


then here is how one can match all those "one letter" followed by a commaaccent and generate a sub (this is a trace of execution, i.e. a copy-paste of what I get on in my shell window):

586 % sed 's/\(.commaaccent\)/sub \1 by \1.alt ;/' test
sub ccommaaccent by ccommaaccent.alt ;
sub gcommaaccent by gcommaaccent.alt ;
sub kcommaaccent by kcommaaccent.alt ;
sub scommaaccent by scommaaccent.alt ;
sub tcommaaccent by tcommaaccent.alt ;


Also, sed allows scripting. Very handy when many substitutions are to be done.

Theunis: I have no specific text editor in mind, however I'm ready invest few bucks if there is one that does the job. I found out that in Windows there is a program called wReplace that does this exact thing.

Michel: Well this is excellent!

sed 's/\([at]\)/\1.alt/g' in.txt

This command seems promising. There are no separate characters I need to replace, they are in long text with complete words, no linebreaks or anything like that. Only thing is that I can't get the slash to work! The output must be: /a.alt

To get /a.alt, you need to "escape" the / in the resulting string, i.e. write \/; here is the trace on in.txt with the line a t a t:

508 % sed 's/\([at]\)/\/\1.alt/g' in.txt
/a.alt /t.alt /a.alt /t.alt


Great! By the way, the pattern \b that matches a word boundary and was used by Theunis above is not available on the Mac sed. If you ever need it or one of the other GNU Sed extensions, you can install gsed from MacPorts, using the line command sudo port install gsed.