variables in bash

Question

for i in *.jpg
do
    j = '$i | cut -d . -f 1'
    convert $i $j".png"
done

temp.sh: line 3: j: command not found

I know about mogrify, just wanted to know how to get variables done in bash.

Answer 1

You have to remove the spaces around =:

for i in *.jpg
do
    j=`echo $i | cut -d . -f 1`
    convert $i $j".png"
done

Answer 2

You can also use bash's builtin parameter expansion to remove the first dot and everything after it: j="${i%%.*}"

If you want to remove the last dot and anything following it (i.e. the file's extension), use: j="${i%.*}"

Example:

$ i="file.with.dots.ext"
$ echo "${i%%.*}"
file
$ echo "${i%.*}"
file.with.dots

Answer 3

In addition, your script won't work as expected if any filename contains any special character (such as a space). You should get in the habit of always enclosing variable references in double quotes. Try this:

for i in *.jpg
do
    j="$(echo "$i" | cut -d . -f 1)"
    convert "$i" "${j}.png"
done