CODEWITHSUNDEEP
bashloopsbrace-expansion
noes
noes

Reputation: 59

Bash: for in loop with brace expansion in list

I would like to write a for in loop in which the possible values are taken from another variable. The part that I can't figure out is how to include values that need brace expansion. For example:

TEXT="a b c d{a..c} e f"
for VAR in $TEXT; do echo $VAR; done

What i get is

a
b
c
d{a..c}
e
f

But what I want is

a
b
c
da
db
dc
e
f

Does anyone know how I can get this to work?

Thank you very much!

Upvotes: 1

Views: 3160

Answers (3)

tavnab
tavnab

Reputation: 2734

EDIT

While there's a time & place for eval, it's not the safest approach for the general case. See Why should eval be avoided in Bash, and what should I use instead? for some reasons why.

Use eval:

TEXT="a b c d{a..c} e f"
for VAR in $TEXT; do eval echo $VAR; done

Output:

a
b
c
da db dc
e
f

If you want to loop over every element, you'll have to nest your loops:

for VAR in $TEXT; do
  for VAR2 in $(eval echo $VAR); do
    echo $VAR2
  done
done

Output:

a
b
c
da
db
dc
e
f

Or use the eval on TEXT rather than each element:

TEXT="$(eval echo "a b c d{a..c} e f")"
for VAR in $TEXT; do echo $VAR; done

Output:

a
b
c
da
db
dc
e
f

Upvotes: 2

Benjamin W.
Benjamin W.

Reputation: 52431

Without eval, but with command substitution:

$ text="$(echo a b c d{a..c} e f)"
$ echo "$text"
a b c da db dc e f

And, as mentioned in Tom's answer, an array is probably the better way to go here.

Upvotes: 0

Tom Fenech
Tom Fenech

Reputation: 74685

I fear that you may have to resort to using eval in this case...However, I'd suggest that you avoided using a loop:

eval "printf '%s\n' $TEXT"

Using eval means that the braces will be expanded, producing your desired outcome.

You can see what happens using set -x:

$ set -x
$ eval "printf '%s\n' $TEXT"
+ eval 'printf '\''%s\n'\'' a b c d{a..c} e f'
++ printf '%s\n' a b c da db dc e f
a
b
c
da
db
dc
e
f

Note that the expansion occurs before the list is passed as arguments to printf.

If you get to define $TEXT yourself and want to loop through each of its expanded elements, I'd suggest using an array instead:

text=( a b c d{a..c} e f )
for var in "${text[@]}"; do
    # whatever with "$var"
done

This is the preferred solution as it doesn't involve using eval.

Upvotes: 5

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