[Solved]Bash:Manipulating arrays of paths? the right way or not?

Question

Note: Refer to the following posts for better solutions and/or alternatives.
This is a mock segment of a script I'm writting and I need to know if I'm doing it the correct way or at least in a proper bash way...
the following works but will it always parse in a sorted manner. I have a set of directories that are named by date in the YYYY-MM-DD (International) format and want to be sure that they will always be treated as directory paths even when special characters "\n,\t,\s ...etc" are encountered in the path. The number of these directories changes and is compared to a set NUM-ber variable and when there are more than the set number the oldest ones are removed which brings a second question. Being dated as YYYY-MM-DD they sort from oldest to newest(lexicographical order) but do they always and is this the right way to deal with elements in an array separated by nulls? Any Comments or suggestions would be appreciated as I'm learning bash for the  time being (perl is next) and gathered this from bits and peices on verious wikis and forums. I basically want know if this a correct approach to the subject of extracting and performing actions on elements of an array that are directory paths.
#!/bin/bash
oifs="$IFS"
IFS=$'\0'
DIRTREE=(/path/to/dated/directories/[0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]/)
NUM=5
HOWMANYMORE=$(echo $(( ${#DIRTREE[@]} - $NUM )))
if (( ${#DIRTREE[@]} > $NUM )) ; then
rm -rv "${DIRTREE[@]:0:$HOWMANYMORE}"
fi
IFS="$oifs"
Note:I have tested this for those wondering
Last edited by Thme (2012-11-30 16:58:13)

Answer 1

aesiris wrote:
there is a special syntax for appending elements to an array:
array+=(element1 element2 ...)
you can simplify to
NUM=3
combined=()
for dir in set1 set2 set3; do
new=(/home/maat/dateddirs/"$dir"/[0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]/)
(( count= ${#new[@]} - NUM ))
combined+=("${new[@]:0:$count}")
done
This works as really well, however, in my case I still need the other sets in separate arrays for other purposes in my personal script so I adapted the approach a little and got this which uses the array+=(foo) syntax properly now. I was aware of this feature in bash arrays and experimented with it but had no success adding elements from other arrays until you demonstrated it in your example by adding them though a "for loop" and doing the arithmetic there... My current one now is very similar...I'm not sure how to reduce it further if possible but I need the other arrays as I do something completely different with them:
#!/bin/bash
NUM=10
set1=(/home/maat/datedfolders/set1/[0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]/)
set2=(/home/maat/datedfolders/set2/[0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]/)
set3=(/home/maat/datedfolders/set3/[0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]/)
CT1=$(( ${#set1[@]} - NUM ))
CT2=$(( ${#set2[@]} - NUM ))
CT3=$(( ${#set3[@]} - NUM ))
for X in "${set1[@]:0:$CT1}" "${set2[@]:0:$CT2}" "${set3[@]:0:$CT3}"
do
combined+=("$X")
done
for
for Xdirs in "${combined[@]}"
do
rm -rv "$Xdirs"
done
I'm considering changing the title of this thread as it reveals a little more than I originally expected to go over and provides some pitfalls as well as ways to approach array manipulation which can be applied to wide range of uses in bash scripting. Others may find totally different uses for what we've discussed here so....
Last edited by Thme (2012-11-30 10:41:02)