This question is different from Execute an array of string describing shell command.
For example, we have an array
myarr=( echo hello you )
How to execute it as one command, i.e. run echo hello you itself?
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1Command as array, command as variable... There are functions for that.Ivan– Ivan2021-09-16 17:55:03 +00:00Commented Sep 16, 2021 at 17:55
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You did not demonstrate that "This question is different from Execute an array of string describing shell command." Execute an array of string describing shell command, So I vote to close it as this exact duplicate. In other words, you made a strong claim that need some strong backing.Léa Gris– Léa Gris2021-09-16 18:58:19 +00:00Commented Sep 16, 2021 at 18:58
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2The other question is related, but not really the same. It is about an array of strings being one full command each. This is about an array of strings that need to put together to make one full command.swingbit– swingbit2021-09-16 19:33:11 +00:00Commented Sep 16, 2021 at 19:33
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@IsaIkari, please review your accepted answer in light of the demonstration at ideone.com/ZVG3uqCharles Duffy– Charles Duffy2021-09-16 19:52:07 +00:00Commented Sep 16, 2021 at 19:52
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2 Answers
To work correctly in all cases, you must put quotes around your expansion.
myarr=( printf ' - %s\n' "first line" "second line" )
"${myarr[@]}"
...correctly writes as output:
- first line
- second line
This DOES NOT WORK if you leave out the quotes. It also does not work if you use eval.
Broken Way 1: Leaving Out Quotes
myarr=( printf ' - %s\n' "first line" "second line" )
${myarr[@]}
...writes only:
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Broken Way 2: Using eval Inappropriately
myarr=( printf ' - %s\n' "first line" "second line" )
eval "${myarr[@]}"
...also writes only:
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Comments
Just use [@] (turn the array into a space-separated string):
$ myarr=( echo hello you )
$ "${myarr[@]}"
hello you
Note: this works, but I would personally find it more correct to use eval:
$ eval "${myarr[@]}"
hello you
EDIT: as pointed out in the comments below, quotes are needed and the solution with eval is not correct, although it works in this case.
6 Comments
Léa Gris
You need double quotes anyway
"${myarr[@]}" or it will split arguments containing spaces, tabs or newlines
swingbit
Thanks, I updated my answer.
Léa Gris
same for the first version without
eval
Charles Duffy
All the advice in this answer, including the version with
eval, is buggy if tested with a more interesting array -- it only appears to work because the sample data is so simple little can go wrong. Try myarr=( printf ' - %s\n' "first word" "second word" ) -- if you run "${myarr[@]}" with the quotes it does the right thing (printing - first word and - second word each on a separate line). It's buggy as eval "${myarr[@]}", and also buggy as ${myarr[@]}. See the above demonstrated at ideone.com/ZVG3uqCharles Duffy
(This happens because when
eval is passed multiple arguments it concatenates them together into a single string, then runs that string through the parser -- so quotes that were consumed in deciding where to divide up eval's arguments are completely discarded. In general, to avoid this class of bug, I always advise that only complete strings be passed to eval). |