Shell Programming and Scripting

Hi. Can somebody please explain the following lines of KSH code for me? The code checks all sub directories in a specific location which are numbered (E.g. test_01, test_02 ... etc.), then finds the one with highest number and extracts that number from the dir name into the variable num. I'd just like to understand how exactly these cmds work. Thanks.

Code:

 
        base=${f##*/} base=${base%_*}
        num=${f##*_}
        (( num > max[$base] )) && max["$base"]=$num

${f##*/} uses Remove matching prefix pattern to expand variable f and remove all characters up to and including the last slash (/) character from the expansion. So if f contains /one/two/three/four the expansion will be four


${base%_*} uses Remove matching suffix pattern to expand variable base and remove all characters from the first underscore (_) to the end of the variable. So if base contains june_1234 the expansion will be june

base=${f##*/} base=${base%_*} This will temperately assign base as per first description and then use this to re-assign it as per the 2nd description. so if f=/one/two/three/a_b_c_123 base will become a_b_c and f will remain unchanged.

num=${f##*_} assign variable num to everything following the last underscore from variable f

(( num > max[$base] )) && max["$base"]=$num If interger comparison of num is greater than array max[$base] then assign max[$base] to num.

Excellent answer. Many thanks.

Just a quick follow up.

This line seems only to calculate up to 10. Afterwards num remains 1 ... it doesn't read the second digit. How can I change this code to increment past 10?

Code:

num=${f##*_} assign variable num to everything following the last underscore from variable f

Thanks a lot.

This seems to be working OK for me:

Code:

for f in  test_1  test_180 test_2 test_10
do
    base=${f##*/} base=${base%_*}
    num=${f##*_}
    (( num > max[base] )) && max[base]=$num
    printf "%d  - %d\n" "$num" "${max[base]}"
done

output:

Code:

1  - 1
180  - 180
2  - 180
10  - 180

Could be if you have some leading zero numbers bash is trying to convert them to octal try:

Code:

for f in  test_0001  test_0180 test_0002 test_0010
do
    base=${f##*/} base=${base%_*}
    ((num=10#${f##*_}))
    (( num > max[base] )) && max[base]=$num
    printf "%d  - %d\n" "$num" "${max[base]}"
done

Thanks. Actually I should add that I'm trying to create a new directory (incrementing it by 1) every time the code runs. E.g. test_1, test_2, test_3 ...
But when it comes to creating the test_10 the directory it fails as it thinks it already exists .. it just sees test_1 again.

Show us the code that you think should do this. Nothing you have shown us makes any attempt to increment anything by 1.