Shell Programming and Scripting

$ echo "[Thr 138] yyeyrtehhehrerry: change this from [Starting steps (10)] to [END (3)]" | nawk awk -F'[' '{$0=$NF ; sub(/ .*/, "") } 1'
END
$

$ echo 'ex.. [Thr 138] yyeyrtehhehrerry: change this from [Starting steps (10)] to END (3)]' | awk -F'[' '{$0=$NF ; sub(/ .*/, "") } 1'
Starting

$ echo 'ex.. [Thr 138] yyeyrtehhehrerry: change this from [Starting steps (10)] to[END (3)]' | sed 's/[^[:alpha:]]/\n/g' | sed  '/^$/d'  | tail -n 1
END

# tested with bash 4 (regex 3.2+)
[[ $string =~  ([[:alpha:]]+).[^[:alpha:]]*$ ]]
echo ${BASH_REMATCH[0]% *}

$ echo 'ex.. [Thr 138] yyeyrtehhehrerry: change this from [Starting steps (10)] to[END (3)]' | sed 's/[^[:alpha:]]/\n/g' | sed  '/^$/d'  | tail -n 1
usage: tail [+/-[n][lbc][f]] [file]
       tail [+/-[n][l][r|f]] [file]

echo 'ex.. [Thr 138] yyeyrtehhehrerry: change this from [Starting steps (10)] to[END (3)]' | sed 's/[^[:alpha:]]/\n/g' | sed  '/^$/d'  | echo 'ex.. [Thr 138] yyeyrtehhehrerry: change this from [Starting steps (10)] to[END (3)]' | sed 's/[^[:alpha:]]/\n/g' | sed  '/^$/d'  | sed -n '$ p'

'ex.. [Thr 138] yyeyrtehhehrerry: change this from [Starting steps (10)] to[END (3)]'