pure shell complex substitution in variable

Question

However it may be impossible, I hope I'm just bad man reader =)

Is there any way to substitute text in variables on several patterns at time or even using back reference?

For example, I have FILE=filename.ext and I want to change it to filename_sometext.ext. But I don't know that file extension is .ext. All I know about it is that extension is after last dot. So I can do it in two steps:

EXT=${FILE##*.}
FILE=${FILE%.*}_sometext.$EXT

Can I do it on one step (smth like ${FILE/.\(*\)/_sometext.\1} [that doesn't work])?

By the way I need to do it in pure shell without sed/awk/etc. My shell is ksh, but if there is way to do it with bashisms I'd like to know it too.

Answer 1

Bash Parameter Expansion says that the variable (FILE in your example) must be a parameter name. So they don't nest. And the last part of ${param/pattern/replacement} must be a string. So back references aren't supported.

My only advice is to use

${EXT:+.$EXT}

to avoid adding a trailing dot if the file has no extension.

---

UPDATE

Apparently back references are supported in ksh93.

So you could use something like

FILE="${FILE/@(.*)/_something\1}"

Answer 2

In this particular case I think FILE=${FILE%.*}_sometext.${FILE##*.} would do the job.