Use bash array as argument

Question

I have the following bash array:

IGNORED_DIRS=(
    "vendor"
    "node_modules"
    "bower_components"
    "tmp"
    "backup"
)

And I need this to be outputted in such a way:

tar -cpzf /var/backups/ --exclude="vendor" --exclude="node_modules" --exclude="bower_components" --exclude="tmp" --exclude="backup"

So far, I have tried the following:

for dir in ${IGNORED_DIRS[@]}
do
    EXCLUDES=$EXCLUDES" --exclude=\""$dir"\""
done

So that I would end up with a variable containing the exact exclude string. I thought I could simply do

tar -cpzf /var/backups/ $EXCLUDES

But that simply ignores all of the exclude flags. Has anyone got the solution for me?

It seems like I've found a solution. Substituting the EXCLUDES line with this EXCLUDES=$EXCLUDES" --exclude="$dir" " seems to fix the issue. So now there are no quotes surrounding the exclude directories anymore. Strange that his does work... — Diederik
– Diederik, Commented Feb 21, 2017 at 20:50
The above only works for trivial cases -- try a directory name with a space. — Charles Duffy
– Charles Duffy, Commented Feb 21, 2017 at 20:59
BTW -- all-caps variable names are used for environment variables and shell builtins with meaning to the operating system or shell, whereas lowercase names are reserved for application use; thus, using lowercase names for your own shell variables means you can't overwrite a variable with meaning to the operating system by mistake -- particularly important if you want your code to be compatible with future OS and shell releases. See relevant spec. — Charles Duffy
– Charles Duffy, Commented Feb 21, 2017 at 21:04

Charles Duffy · Accepted Answer · 2017-02-21 21:00:41Z

4

This is covered in detail in BashFAQ #50. To summarize a solution:

extra_args=( )
for dir in "${IGNORED_DIRS[@]}"; do
    extra_args+=( --exclude="$dir" )
done

tar -cpz "${extra_args[@]}" -f /var/backups/

edited Feb 21, 2017 at 21:00

answered Feb 21, 2017 at 20:54

Charles Duffy

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2 Comments

RavinderSingh13 Over a year ago

Awesome answer.

gniourf_gniourf Over a year ago

Or, simpler, tar -cpz "${IGNORED_DIRS[@]/#/--exclude=}" -f /var/backups.

Charles Duffy · Accepted Answer · 2017-02-22 04:23:44Z

1

Modifying @favoretti's response, use (..) to collect the array and ${array[@]} to expand the array into items, rather than joining into one string.

IGNORED_DIRS=(
    "vendor"
    "node_modules"
    "bower_components"
    "tmp"
    "backup"
)

for dir in "${IGNORED_DIRS[@]}"
do
    EXCLUDES=("${EXCLUDES[@]}" --exclude="$dir")
done

tar -cf /var/backup "${EXCLUDES[@]}"

edited Feb 22, 2017 at 4:23

Charles Duffy

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answered Feb 21, 2017 at 20:56

Joshua Goldberg

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5 Comments

favoretti Over a year ago

Primarily it needs ${EXCLUDES[@]} in the right spot in the tar command itself. Whether bash syntax is correct or less correct.

Diederik Over a year ago

Thanks so much guys. Learning a lot!

Charles Duffy Over a year ago

GNU tar is flexible on the point, but it goes beyond POSIX spec in that. (Though admittedly, --exclude is out-of-spec as well).

Charles Duffy Over a year ago

re: options-before-positional-arguments, see POSIX utility syntax guidelines, guideline #9.

Charles Duffy Over a year ago

@JoshuaGoldberg, do you mind if I make the minimum necessary edits to fix the bugs?

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