[SOLVED] Loop through unknown number of folders with progressive names

Issue

I am trying to use the bash to loop through an unknown number of folders which end with a progressive number starting from 0. Each folder is named processor* where * stands for the progressive number (e.g. processor0, processor1, processor2, etc..). Inside each loop the script should execute these commands find ./ -name 'U' | while read U ; do cp "$U" ./0 ; done.

My for loop looks like this:

for i in processor*; do
    cd ./processor$i
    find ./ -name 'U' | while read U ; do cp "$U" ./0 ; done
    cd ..
done

but it currently does not work.

Solution

When you use the syntax for i in processor*, the results of expanding processor* will be iterated over, and the variable i will hold the result for a given iteration.

From the GNU HTML manual for bash:

The syntax of the for command is:
for name [ [in [words …] ] ; ] do commands; done
Expand words (see Shell Expansions), and execute commands once for each member in the resultant list, with name bound to the current member.

For example, if the current working directory contained the directories processor0, processor1, and processor_something_else, and the expansion of processor* was in that order, then i will have the following value for the separate iterations:

• i has the value processor0 in the first iteration
• i has the value processor1 in the second iteration
• i has the value processor_something_else in the second iteration

The expression ./processor$i then would evaluate to the following in each iteration:

• ./processorprocessor0
• ./processorprocessor1
• ./processorprocessor_something_else

This is because the value of i will be expanded as the cd command is generated.

What you really want is to use cd ./"$i".

Answered By - Shane Bishop