Unix Power Tools
Making a for Loop with Multiple Variables

The normal Bourne shell for loop lets you take a list of items, store the items one by one in a shell variable, and loop through a set of commands once for each item:

for file in prog1 prog2 prog3

do

    ...process $file   

done

I wanted a for loop that stores several different shell variables and makes one pass through the loop for each set of variables (instead of one pass for each item, as a regular for loop does). This loop does the job:

for bunch in "ellie file16" "donna file23" "steve file34"

do

   # PUT FIRST WORD (USER) IN $1, SECOND (FILE) IN $2...

   set $bunch

   mail $1 < $2

done

If you have any command-line arguments and still need them, store them in another variable before you do that. Or, you can make the loop this way:

for bunch in "u=ellie f=file16 s='your files'" \

    "u=donna f=file23 s='a memo'" "u=steve f=file34 s=report"

do

   # SET $u (USER), $f (FILENAME), $s (SUBJECT):

   eval $bunch

   mail -s "$s" $u < $f

done

This script uses the shell's eval command to re-scan the contents of the bunch variable and store it in separate variables. Notice the single quotes like s='your files'; this groups the words for eval. The shell removes those single quotes before it stores the value into the s variable.

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