Modify a path stored in a bash script variable - bash

Question

I have a variable f in a bash script
f=/path/to/a/file.jpg
I'm using the variable as an input argument to a program that requires and input and an output path.
For example the program's usage would look like this
./myprogram -i inputFilePath -o outputFilePath
using my variable, I'm trying to maintain the same basename, change the extension, and put the output file into a sub directory. For example
./myprogram -i /path/to/a/file.jpg -o /path/to/a/new/file.tiff
I'm trying to do that by doing this
./myprogram -i "$f" -o "${f%.jpg}.tiff"
of course this keeps the basename, changes the extension, but doesn't put the file into the new subdirectory.
How can I modify f to to change /path/to/a/file.jpg into /path/to/a/new/file.tiff?

Answer 1

Actually you can do this in several ways:
Using sed as pointed out by #anubhava
Using dirname and basename:
./myprogram -i "$f" -o "$(dirname -- "$f")/new/$(basename -- "$f" .jpg).tiff"
Using only Bash:
./myprogram -i "$f" -o "${f%/*}/new/$(b=${f##*/}; echo -n ${b%.jpg}.tiff)"
Note that unlike the second solution (using dirname/basename) that is more robust, the third solution (in pure Bash) won't work if "$f" does not contain any slash:
$ dirname "file.jpg"
.
$ f="file.jpg"; echo "${f%/*}"
file.jpg

Answer 2

You may use this sed:
s='/path/to/a/file.jpg'
sed -E 's~(.*/)([^.]+)\.jpg$~\1new/\2.tiff~' <<< "$s"
/path/to/a/new/file.tiff

Answer 3

If you're on a system that supports the basename and dirnamecommands you could use a simple wrapper function eg:
$ type newSubDir
newSubDir is a function
newSubDir ()
{
oldPath=$(dirname "${1}");
fileName=$(basename "${1}");
newPath="${oldPath}/${2}/${fileName}";
echo "${newPath}"
}
$ newSubDir /path/to/a/file.jpg new
/path/to/a/new/file.jpg
If your system doesn't have those, you can accomplish the same thing using string manipulation:
$ file="/path/to/a/file.jpg"
$ echo "${file%/*}"
/path/to/a
$ echo "${file##*/}"
file.jpg