chainlinks

#!/bin/bash -eu

#so I needed to test something with a symlink chain, after a while I figured it's going to be quicker to write a script for it than generating symlinks by hand
#you need to provide 2 positive integer numbers as commandline parameters like this:
#$ chainlinks 3 4
#the first one is going to be the number of links generated per subdirectories
#the second one is going to be the depth of the subdirectory chain
#chainlinks 5 5 generates a chain of symlinks in a way that 1306 symlinks need to be resolved to get to the actual file referenced (unless you use some elaborate mapping to deal with chains and multiple traversals of the same symlinks)
#for chainlinks 6 6 this number pops up to 50431
#
#so this is how it's used:
#$ rm -r abcmy*
#$ pwd
#/tmp
#$ ./chainlinks 6 6
#$ cat abcmywhatsthis.txt
#cat: abcmywhatsthis.txt: Too many levels of symbolic links
#$ time readlink -f abcmywhatsthis.txt
#/tmp/abcmydir/abcmydir/abcmydir/abcmydir/abcmydir/abcmydir/abcmyfile.txt
#
#real  0m3,228s
#user  0m2,283s
#sys   0m0,945s
#$ cat `readlink -f abcmywhatsthis.txt`
#Hello symlinked world!
#$ rm -r abcmy*
#$ ./chainlinks 7 7
#$ time readlink -f abcmywhatsthis.txt
#/tmp/abcmydir/abcmydir/abcmydir/abcmydir/abcmydir/abcmydir/abcmydir/abcmyfile.txt
#
#real  1m13,051s
#user  0m53,812s
#sys   0m19,235s
#$ rm -r abcmy*
#$ ./chainlinks 10 10
#$ du -hc abcmy*|grep total
#348K  total


function isnum()
{
  local ret=0
  echo "$1"|grep -qE '^(0|[1-9][0-9]*)$' || ret=$?

  if [[ $ret -ne 0 ]]
   then
    echo "$2 needs to be a number!" >&2
    exit 1
   fi

  if [[ ( $# -gt 2 ) && ( $1 -lt $3 )]]
   then
    echo "$2 needs to be greater than $3!" >&2
    exit 1
   fi
}

function chainlinks()
{
  local prefix=abcmy
  #we know for sure that none of my variables will contain any characters which bash is sensitive to, therefore I can safely refrain from quoting anything:
  local linkcount=$1
  shift
  local depth=$1
  shift
  local back=${1:-}
  local target

  if [[ $depth -eq 0 ]]
   then
    target=${prefix}file.txt
    echo "Hello symlinked world!" >$target
    date >>$target
   else
    target=${prefix}dir
    mkdir $target
   fi

  local origtarget=$target
  local mylinkcount=$linkcount

  while [[ $mylinkcount -gt 0 ]]
   do
    local newtarget=${prefix}link$mylinkcount
    mylinkcount=$[ mylinkcount - 1 ]
    ln -s $back$target $newtarget
    target=$newtarget
   done

  if [[ $depth -gt 0 ]]
   then
    cd $origtarget
    back=../${back}${prefix}link1/
    chainlinks $linkcount $[ depth - 1 ] $back
    cd ..
   fi

  local mydepth=$depth
  local whatsthis=""

  while [[ $mydepth -ge 0 ]]
   do
    whatsthis=/${prefix}link1$whatsthis
    mydepth=$[ mydepth - 1 ]
   done

  ln -s .$whatsthis ${prefix}whatsthis.txt
}

isnum "$1" "linkcount (1st parameter)" 1
isnum "$2" "depth (2nd parameter)"
chainlinks $1 $2 || exit $? ; exit 0