Re: nested loops: '; done ; done' vs. '; done done'
- From: Kaz Kylheku <kkylheku@xxxxxxxxx>
- Date: Tue, 05 Jun 2007 17:23:20 -0000
On Jun 2, 1:36 am, Frank Terbeck <f...@xxxxxxxxxxxxxxxxxxx> wrote:
Hello,
When nesting two for-loops, why does the following work?
for i in a b c ; do for e in x y z ; do echo $i$e ; done done
This is analogous to closing nested if's with fi fi fi ...
These keywords terminate the command, making it lexically clear that
the following material is the start of another command without the
need for a separating semicolon.
I was sure it had to be '; done ; done' at the end (which, of course,
works as well). But I tried the former in various shells (old-bourne,
ash, ksh93, zsh, bash...) and it always works. :-)
It's perfectly clear in the grammar given in the Single Unix
Specification.
The specific phrase rule which generates your above for_clause is:
for name linebreak in wordlist sequential_sep do_group
Thus the nested for is generated by the do_group, which is:
do compound_list done
The compound_list isn't required to generate a terminating semicolon.
A simple loop terminated by done counts, grammatically, as a compound
list. The precise derivation chain is:
compound_list
-> and_or
-> pipeline
-> pipe_sequence
-> command
-> compound_command
-> for_clause
And so you have ``do for_clause done'', which generates the done done.
That's a wrap! :)
.
- References:
- nested loops: '; done ; done' vs. '; done done'
- From: Frank Terbeck
- nested loops: '; done ; done' vs. '; done done'
- Prev by Date: Variable substitution
- Next by Date: Re: Pick 8-bit ascii using awk
- Previous by thread: Re: nested loops: '; done ; done' vs. '; done done'
- Next by thread: Pick 8-bit ascii using awk
- Index(es):
Relevant Pages
|
