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I am trying to learn loops and array manipulation in zsh.

Say I have two arrays in zsh with the same unknown # of elements and each of them containing a list of paths, e.g.


I would like to iterate through both arrays simultaneously with a common index, so that I can do something like:

hg pull $REMOTE_PATH_i

in each iteration. How can I do this in zsh?

Also, I have searched for loop control and arrays in the zsh documentation but had little success. Is there a good tutorial that introduces the basics of loops, arrays, etc. in zsh? Something for people with little bash or shell-scripting experience but with a background in programming?

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1 Answer 1

up vote 6 down vote accepted

Section 15.2.1 “Array Subscripts” says that arrays can be index with [exp] (where exp is a numeric expression) and that elements start at index 1 (0 if KSH_ARRAYS is set).

Section 14.3 “Parameter Expansion” says that the syntax ${#array_name} will expand to the number of elements of an array.

Section 6.3 “Complex Commands” gives the syntax for a numeric for loop (as in C):
for (( initExpr ; testExpr ; stepExpr )) do … done.

Putting them all together:

for (( i = 1; i <= $#LOCAL_PATH; i++ )) do
    ( # subshell to contain the effect of the chdir
        cd $LOCAL_PATH[i]
        hg pull $REMOTE_PATH[i]

Or, if you are using KSH_ARRAYS, then this:

for (( i = 0; i < ${#LOCAL_PATH[*]}; i++ )) do
    ( # subshell to contain the effect of the chdir
        cd ${LOCAL_PATH[i]}
        hg pull ${REMOTE_PATH[i]}

Using KSH_ARRAYS makes arrays start with index 0, requires the use of braces for array expressions, and interprets $array as $array[0] (requiring a change to the array length expression). The syntax changes required by KSH_ARRAY will also work without KSH_ARRAY, but you still have to adjust the logic for the different index range (1 through N versus 0 through N-1).

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