shell - To pick certain entries from a file in unix -

i have text file 4 entries. when run shell script first time, first entry should picked . when run 2nd time, 2nd entry should picked , when run script 5th time again 1st entry should picked up.

basically should pick entries in text file 1 one , when reaches last , again should start first.

i thought of keeping 1 more file , current running entry , when runs next time check file , process next line. cannot keep files. logic should handled inside script without keeping other files.

i hope explained problem.. please me logic in unix ..

you can use trap in brute force call sed update index within file on termination or exit. example:

#!/bin/bash  declare -i current_idx=0  trap 'sed -i "s/^declare[ ]-i[ ]current_idx[=].*$/declare -i \ current_idx=$(((current_idx+1) % 4))/" $(readlink -f "$0")' sigterm exit  case "$current_idx" in     0 ) printf "picked %d entry\n" "$current_idx";;     1 ) printf "picked %d entry\n" "$current_idx";;     2 ) printf "picked %d entry\n" "$current_idx";;     3 ) printf "picked %d entry\n" "$current_idx";;     * ) printf "error: current_idx '%d'\n" "$current_idx";; esac 

example use

here script called 11 times showing how cycles through 4 different entries returning first on 5th call.

$ (for in {0..10}; bash selfmod.sh; done) picked 0 entry picked 1 entry picked 2 entry picked 3 entry picked 0 entry picked 1 entry picked 2 entry picked 3 entry picked 0 entry picked 1 entry picked 2 entry 

note: self-modifying script isn't practice. separate-file idea safer. however, purposes, work. however, make no representation how wise or safe is.