12

When you use brace expansion in bash, something like

echo {a,b,c}

becomes

echo a b c

Is there a way to expand it to 3 separate commands, one for each expansion, instead?

So that:

echo {a,b,c}

would become

echo a
echo b
echo c
houbysoft
  • 4,444

4 Answers4

13

Is this just a "because I wanna know" question, or is there a real use case for it? We could go through some gymnastics to get it done:

$ eval echo\ {a,b,c}\;
a
b
c

But I'd hunt down anyone that was putting in these kinds of obfuscatory commands into our system scripts.

Why not go for clarity instead:

$ for X in {a,b,c}; do echo $X; done

You could even go whole-hog and put in a couple of newlines and indent it a bit so that you'd always be able to understand what you were trying to do.

unpythonic
  • 301
3

Based on Mark Mann's selected answer, I was able to further derive this example, which works great:

$ eval echo\ category_{17,32,33}.properties\{,.bak\}\;
category_17.properties category_17.properties.bak
category_32.properties category_32.properties.bak
category_33.properties category_33.properties.bak

What that is showing, is when you are using multiple occurrences of brace expansion within a line, Mark's original example would have printed every variation individually. Instead, I wanted to use his answer to move/rename multiple files. To ensure that the output matched the format that mv normally expects (mv oldfilename newfilename), I escaped the second occurrence of brace expansion, so that it wouldn't be evaluated until after the initial eval command had executed.

As the above output appeared as expected, I was then able to run the following command:

$ eval mv\ category_{17,32,33}.properties\{,.bak\}\;
$ ls
category_17.properties.bak  category_32.properties.bak  category_33.properties.bak

Many thanks to Mark for his original answer. Please up-vote his answer if you like what his answer allowed me to do :-)

Community
  • 1
Jon L.
  • 133
1
$ echo {a,b,c} | xargs -n1
a
b
c
promaty
  • 11
0
printf '%s\n'  echo{\ a,\ b,\ c}
tae
  • 1