I'm trying to declare an empty array in Shell Script but I'm experiencing an error.
#!/bin/bash
list=$@
newlist=()
for l in $list; do
newlist+=($l)
done
echo "new"
echo $newlist
When I execute it, I get test.sh: 5: test.sh: Syntax error: "(" unexpected
In BASH 4+ you can use the following for declaring an empty Array:
declare -a ARRAY_NAME=()
You can then append new items NEW_ITEM1 & NEW_ITEM2 by:
ARRAY_NAME+=(NEW_ITEM1)
ARRAY_NAME+=(NEW_ITEM2)
Please note that parentheses () is required while adding the new items. This is required so that new items are appended as an Array element. If you did miss the (), NEW_ITEM2 will become a String append to first Array Element ARRAY_NAME[0].
Above example will result into:
echo ${ARRAY_NAME[@]}
NEW_ITEM1 NEW_ITEM2
echo ${ARRAY_NAME[0]}
NEW_ITEM1
echo ${ARRAY_NAME[1]}
NEW_ITEM2
Next, if you performed (note the missing parenthesis):
ARRAY_NAME+=NEW_ITEM3
This will result into:
echo ${ARRAY_NAME[@]}
NEW_ITEM1NEW_ITEM3 NEW_ITEM2
echo ${ARRAY_NAME[0]}
NEW_ITEM1NEW_ITEM3
echo ${ARRAY_NAME[1]}
NEW_ITEM2
Thanks to @LenW for correcting me on append operation.
ARRAY_NAME+=(NEW_ITEM1 NEW_ITEM2). So you're really just concatenating two arrays. This is also possible when not specifying either array as a literal, though the syntax gets a bit clunky in that case: ARRAY1+=(${ARRAY2[@]}).Run it with bash:
bash test.sh
And seeing the error, it seems you're actually running it with dash:
> dash test.sh
test.sh: 5: test.sh: Syntax error: "(" unexpected
Only this time you probably used the link to it (/bin/sh -> /bin/dash).
bash script.sh worked. But ... why even with #!/bin/bash it executes on dash? I typed export and my SHELL is set to bash.
sh. You can see where it is pointing to with ls -l /bin/sh or readlink $(which sh). By the way, the quickest way to declare your array variable newlist based from your arguments is newlist=("$@"). Note that if args is "a b" "c" "d", without quotes ($@) it would split to 4 arguments when expanded ("a" "b" "c") due to word splitting whereas with "$@" the values remain as is with space.
#! only works if you run it as a command - by making the file executable (chmod +x test.sh) and then just typing the filename without any sort of *sh in front of it: ./test.sh. If you explicitly type the name of a shell like sh or bash as the command to run, then that's the command that gets run; and to a shell, the #! line is just a comment../test.sh but dash is still the one that has executed/bin/sh is linked to, because the shebang line has /bin/bash in it.I find following syntax more readable.
declare -a <name of array>
For more details see Bash Guide for Beginners: 10.2. Array variables.
Try this to see if you are oriented to dash or bash
ls -al /bin/sh
If it says /bin/sh -> /bin/dash, then type this:
sudo rm /bin/sh
sudo ln -s /bin/bash /bin/sh
Then type again:
ls -al /bin/sh*
then must says something like this:
/bin/sh -> /bin/bash
It means that now sh is properly oriented to Bash and your arrays will work.
DOMAINS=(1); if [[ ${DOMAINS-} ]]; then # true
unset DOMAINS; if [[ ${DOMAINS-} ]]; then # false
If the array is empty just do this:
NEWLIST=
You can check it with:
if [ $NEWLIST ] ; then
# do something
fi
a non empty array declaration looks like this:
NEWLIST=('1' '2' '3')
To fill an array during process:
ARRAY=("$(find . -name '*.mp3')")
Hope this helps
NEWLIST has length 1 in that example. Try echoing ${#NEWLIST[@]} afterwards to see this.
NEWLIST is not an empty array, because it has length 1. I'm sorry, but you haven't answered the question correctly. Your if statement doesn't test for this properly.
bash? It looks like the script is being run usingsh, in which case arrays are not supported.$@to another parameter loses the benefits of$@, namely that white-space within a single command line argument is preserved. Ditchlistand usefor l in "$@"; dodirectly.