bash function : splitting name and extension of a file

Question

I have the following function split in my .bash_profile file.

function split {
   name="${$1%.*}"
   ext="${$1##*.}"
   echo filename=$name extension=$ext
}

Now I should expect that the command split foo.bar will give me

filename=foo  extension=bar

But I get get -bash: ${$1%.*}: bad substitution error message. The same however works for usual shell variable in a shell script, say $x instead of $1 in .bash_profile (I think the same goes in .bashrc as well).

What's wrong and any remedy?

And you do need quotes where you are passing variables to the echo command. — Wildcard, Sep 28 '16 at 20:09
@Wildcard Maybe grammatically I need to quote after echo. But without quote works in many shells. Also I may skip quotes for variables name and ext as already pointed out by @SatoKatsura. — hbaromega, Sep 28 '16 at 21:40
No, it doesn't "work," it does something else entirely. Your variables will be word split and subjected to glob expansion. Only by accident will you get the results you expect. See Why does my shell script choke on whitespace or other special characters? and Security implications of forgetting to quote a variable in bash/POSIX shells. — Wildcard, Sep 28 '16 at 22:32

score 5 · Accepted Answer · answered Sep 28 '16 at 20:02

5

Drop the $ preceding the variable name (1) inside the parameter expansion:

name="${1%.*}"
ext="${1##*.}"

you are already referring to the variable with the $ preceding the starting brace {, no need for another one in front of the variable name.

answered Sep 28 '16 at 20:02

heemayl

56,300

Also, you don't need quotes in the right-hand side of assignments. – Satō Katsura Sep 28 '16 at 20:26
@SatoKatsura That's true. – heemayl Sep 28 '16 at 20:27
@SatoKatsura Yeah realized that too. Thanks. – hbaromega Sep 28 '16 at 21:41

score 1 · Answer 2 · answered Sep 28 '16 at 20:43

If you have the dirname, basename and awk commands, you might want to consider this function definition

function split {

DIR=$(/bin/dirname "$1")
BASE=$(/bin/basename "$1")
EXT=$(echo "$BASE" | /usr/bin/awk -F. 'NF>1 {print $NF}')
NAME=${BASE%.$EXT}
echo directory=$DIR filename=$NAME extension=$EXT

}

split good.bye/data.txt
split good.bye/data
split data.txt
split good.bye/data.001.txt
split "good bye/data 001.txt"

bash function : splitting name and extension of a file

2 Answers2