Bash: Nested variable expansion

Question

How can I nest operations in bash? e.g I know that

$(basename $var)

will give me just the final part of the path and

${name%.*}

gives me everything before the extension.

How do I combine these two calls, I want to do something like:

${$(basename $var)%.*}

It appears that none of the answers addresses the "real" question, i.e. is nested variable expansion possible? Without using a command line tool like `basename`. — Nikos Alexandris, Dec 05 '18 at 15:37
Here an answer (though not the accepted one): https://stackoverflow.com/a/6724305/1172302 — Nikos Alexandris, Dec 05 '18 at 15:38

score 2 · Accepted Answer · answered Oct 29 '18 at 13:24

As @sid-m 's answer states, you need to change the order of the two expansions because one of them (the % stuff) can only be applied to variables (by giving their name):

echo "$(basename "${var%.*}")"

Other things to mention:

You should use double quotes around every expansion, otherwise you run into trouble if you have spaces in the variable values. I already did that in my answer.
In case you know or expect a specific file extension, basename can strip that off for you as well: basename "$var" .txt (This will print foo for foo.txt in $var.)

score 1 · Answer 2 · answered Oct 29 '18 at 13:08

1

You can do it like

 echo $(basename ${var%.*})

it is just the order that needs to be changed.

answered Oct 29 '18 at 13:08

sid-m

1,396
11
19

Thanks, that worked. Can you explain the logic why it has to be that way around? – Rizhiy Oct 29 '18 at 13:11
The `echo` is unnecessary; `basename "${var%.*}"` does the same thing.. – chepner Oct 29 '18 at 13:47

score 0 · Answer 3 · answered Oct 29 '18 at 13:04

0

Assuming you want to split the file name, here is a simple pattern :

$ var=/some/folder/with/file.ext
$ echo $(basename $var) | cut -d "." -f1
file

answered Oct 29 '18 at 13:04

chenchuk

4,664
4
28
39

score 0 · Answer 4 · answered Oct 29 '18 at 13:46

If you know the file extension in advance, you can tell basename to remove it, either as a second argument or via the -s option. Both these yield the same:

basename "${var}" .extension
basename -s .extension "${var}"

If you don't know the file extension in advance, you can try to grep the proper part of the string.

### grep any non-slash followed by anything ending in dot and non-slash
grep -oP '[^/]*(?=\.[^/]*$)' <<< "${var}"

Bash: Nested variable expansion

4 Answers4