Script to cycle through a list of files, setting a symlink to the next file in the list

cycleCreds.sh

#!/bin/sh
# I had a bunch of credentials files in a directory, and wanted to be able to
# cycle quickly between them so that I could log into a service with different
# identities. This script does the job by creating a symlink:
#     credentials => creds.foo
# Every time you call it, it sets the symlink to the next file in the list.
# It's probably way overkill, but it was an interesting learning exercise writing it!
# This may need tweaking to work on your version of Linux.

setlink() {
  rm -f credentials
  ln -s $1 credentials
  echo "Using $1"
}

credfiles=(`ls creds.*`)
len=${#credfiles[@]}
curr=$(readlink -n 'credentials')
if [ "X$curr" = "X" ] ; then
  # Symlink doesn't exist, arbitrarily set it to first creds file in list.
  setlink ${credfiles[0]}
  exit
fi
for (( ii = 0 ; ii < $len ; ++ii )); do
  if [ "$curr" = "${credfiles[$ii]}" ] ; then
    next=$(( ($ii+1) % $len ))
    setlink ${credfiles[$next]}
    break
  fi
done