1

In Bash,

  1. the syntax of the C-like for-loop is:

    for (( expr1 ; expr2 ; expr3 )) ; do commands ; done

    Can the execution of commands affect the evaluations of the three arithmetic expressions expr1, expr2, and/or expr3, and therefore change the iterations (e.g. the number of iterations)?

    Or are the iterations (e.g. the number of iterations) unaffected by execution of commands in each iteration?

  2. The other syntax of the for command is:

    for name [ [in [words ...] ] ; ] do commands; done

    Can execution of commands in each iteration affect the iterations (e.g. the number of iterations)?

Improve this question

1 Answer 1

Reset to default
3

Sure:

$ bash -c 'for ((i=0;i<10;i++)); do echo $i; ((i++)); done'
0
2
4
6
8

In the for ((expr1; expr2; expr3) form, expr2 (and expr3, if expr2 didn't fail) are evaluated each time the loop is run. With the other form, bash starts the loop after words have been expanded (that includes performing command substitution, globbing, etc.). So you can't affect the possible values of the iteration variable (name) once the loop starts. You can, of course:

$ bash -c 'for i; do echo $i; break; done' _ a b c
a
Improve this answer
4
  • Thanks. How about the same questions for the other syntax of for-loop? Commented Apr 24, 2016 at 15:52
  • @Tim see update Commented Apr 24, 2016 at 16:00
  • what does _ mean in bash -c 'for i; do echo $i; break; done' _ a b c? Commented Apr 24, 2016 at 16:05
  • _ is $0 in this case. Since for i only loops from the first argument, I used _ as placeholder. unix.stackexchange.com/q/152391/70524 Commented Apr 24, 2016 at 16:06

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.