UNIX for Dummies Questions & Answers

Is there a Unix command similar to the WHERE command in IDL. Such a command would return all location numbers of an array where the value at those locations satisfy specified conditions. For example, if I have a random vector

vector=(3 5 6 9)

how can I find the location numbers in ${vector} corresponding to values less gt 3 and lt 9.

What should be returned is a two-element vector: (1 2)

How can I get Unix to do this?

How do you mean - get UNIX to do this? perl, python, ruby, etc. all can do something like this for you with a small bit of programming, if you want C or shell script you have to roll your own.. We'll help, just let us know what you need.

Hi,

I would like to have this within a bash shell script. This would allow me to get around some scripting trouble that nobody has been able to sufficiently help with yet. I have a directory containing multiple files, all of similar construct:
A2008196231000.L2

I am only interested in digits 6-8, so the filenames are effectively:
?????---* (where the three digits --- represent the year day of the file)

I have files ranging from ?????001* to ?????366*. How can I list all the files within a certain range of days? The fact that the year days must be three digits long (001 to 366) makes this difficult.

If anyone could help with that, it would be great! The reason I would like a WHERE statement would be to get around this. Perhaps I could create an array, where each element is a different filename in the directory. Then I would create another array of the same size, where each element is the three digit year day of the file in the initial array. Then I could find out which elements of this array are -gt or -lt bounds that I specify, and use the returned array locations to subset the initial array. Is that possible in a bash shell script?

One way ........

Output all the files for day 12 through day 40

Code:

start=12
end=40

for ((i=start ; i<=end ; i++))
do
  j=${j}$(printf "%03i,\n" ${i} )
done
j=${j%,}

ls A2008{$j}*.L2 2>/dev/null

Hi,

Thank you very much for the reply! I am very new to Unix.

- Could you explain the statement within the for loop?
- What is the meaning of 2>/dev/null?
- Will this work with 3-digit days (001-365)?

Thanks again. I really appreciate the help.

2> /dev/null means that anything written to stderr by the ls(1) command (typically error messages such as could not find a matching file) is not displayed.

Yes this code works with 3 digit days.

If your condition can be covered by a simple wildcard, use that. For example, the following will match all files between 010 and 029.

Code:

A20080[12][0-9]231000.L2