Linux shell environment variable

[aniecki]

I am trying to set a PREFIX variable in a bash command line, say
echo $PREFIX
CA_RA
Yet when trying to rename a file, it gives
Tag 'PREFIX' not defined ,
as in the command

exiftool '-testname<$PREFIX-%.4nC.%e'  .

This way would be easier to update bunch of files, not to change the PREFIX on the command.
Thanks!

[Phil Harvey]

The shell does not interpolate within single quotes.  Use double quotes instead if you want to use shell variables.

- Phil

[aniecki]

exiftool "-testname<$PREFIX-%.4nC.%e"  .

Warning: Invalid tag name 'l-nl_cl-%.4nc.%e'

still, seems not to be working...

[StarGeek]

This is Common Mistake #5c.  You are not copying any tags, you are setting TestName a static value.  Try this
exiftool "-testname=$PREFIX-%.4nC.%e"  .

[Phil Harvey]

(I should have caught this)

[aniecki]

Is there a way to combine two, eg.

(These do not work, only examples)
exiftool "-testname=$PREFIX-<${Megapixels}%.4nC.%e"  .
exiftool "-testname=$PREFIX" '-testname<${Megapixels}%.4nC.%e'  .

to give outcome:
'./CA_RA-0.110-0001.jpeg'

If this cannot be done in one go, I would run it twice. The second run to skip x-length charters at the beginning of a picture file, if that would be easier.
But perhaps a way to achieve it in one run..

Thanks!

[Phil Harvey]

There are a number of ways to do this.  With bash, escaping "$" in the non-shell variable should work like this:

exiftool "-testname<$PREFIX-\${Megapixels}%.4nC.%e" .

You could also change from double to single quotes:

exiftool "-testname<$PREFIX"'-${Megapixels}%.4nC.%e' .

- Phil

[aniecki]

Thanks guys, indeed both ways work!