Zsh brace expansion and inline for loops

Two tips for today: zsh brace expansions [1] [2] and short for loops.

Brace Expansion:
{x..y} will expand to the integers x,x+1,...y. Prepend the numbers with padding for padded output. This will work in bash as well.

echo {3..5}     # 3 4 5
echo {3..100}   # 3 4 5 ... 10 11 12 ... 98 99 100
echo {03..100}  # 03 04 05 ... 10 11 12 ... 98 99 100
echo {003..100} # 003 004 005 ... 010 011 012 ... 098 099 100

Up until now, I've used seq to create integer lists like this. Using seq in commands requires a subshell. Do you know how to zero-pad the output of seq?

echo $(seq 3 5)   # 3 4 5
echo $(seq -w 3 5) # 3 4 5
echo $(seq -w 8 10) # 08 09 10

But today is about moving beyond seq. Let's move on to for loops.

For Loops:

% for i in {3..5}; do echo $i; done
3
4
5

Zsh has two shortened forms of this standard for loop. The short forms only support a single command. If you really want multiple commands, you can put them in {}, but then you might as well use "do ... done" in that case. These won't work in bash (woo!).

I never remember this when I need it and can't find references to this zsh specific "single line forloop" -- but it's right there in zshmisc,"Alternate Forms For Complex Commands."

for ... in list; comand
for ... (list) command

# short form with "in" and ";"
% for i in {3..5}; echo "line $i"; date
line 3
line 4
line 5
Fri May 11 15:52:32 PDT 2012

# short form with parens:
% for i ({3..5}) echo "line $i"; date
line 3
line 4
line 5
Fri May 11 15:52:32 PDT 2012

# short form with multiple commands in {}
% for i in {3..5}; { echo "line $i"; date }
line 3
Fri May 11 15:52:43 PDT 2012
line 4
Fri May 11 15:52:43 PDT 2012
line 5
Fri May 11 15:52:43 PDT 2012

Complex Commands
for name ... [ in word ... ] term do list done

where term is at least one newline or ;. Expand the list of words, and set the parameter name to each of them in turn, executing list each time. If the in word is omitted, use the positional parameters instead of the words.

More than one parameter name can appear before the list of words. If N names are given, then on each execution of the loop the next N words are assigned to the corresponding parameters. If there are more names than remaining words, the remaining parameters are each set to the empty string. Execution of the loop ends when there is no remaining word to assign to the first name. It is only possible for in to appear as the first name in the list, else it will be treated as marking the end of the list.

Alternate Forms For Complex Commands

for name ... ( word ... ) sublist

A short form of for.

for name ... [ in word ... ] term sublist

where term is at least one newline or ;. Another short form of for.