How to process every second file in bash?

Question

I have a directory with a few dozens of files. I would like to do something with every second file from this directory. By now I only used find command but with thi

Answer 1

cnt=0; 
for file in $(find ./dir -type f); <-- if not too many matches
do 
  let cnt=cnt+1; 
  if [ $cnt -eq 2 ]; 
    then echo $file;               <-- do something
    cnt=0;                         <-- alternate file
  fi; 
done

or

second_file=$(find -type f | head -2 | tail -1);

Answer 2

I had every file twice, and needed to delete every second file. Find just returned me random files, therefore I added a sort. It now looks like this:

#!/bin/bash
DIRNAME="<directoryNameContainingYourFiles>"
for file in `find $DIRNAME -type f | sort | awk 'NR % 2 == 0'`; do
  echo "going to modify" $file
  #  ls -laFh $file           # show file details
  #  rm $file                 # delete file
  #  mv $file <newDirName>    # move file to <newDirName>
done

put this in a file called scriptName, run

chmod +x scriptName

and start it by calling

./scriptName

Answer 3

If you want to run my_cmd on each of the alternate file, this may help

 find ./dir -type f | sort -n | sed -n '1~2!p'  | sed 's/^/mycmd  /' | sh

I've copied the sed from How to remove every other line with sed?

Answer 4

for file in `find dir -type f | awk 'NR % 2 == 0'`; do
  echo $file
done

NR is the current row number. To get odd rows, use ... == 1.