Linux で文字列が数値かどうかを判断する方法

a=1234
echo "$a"|[ -n "`sed -n '/^[0-9][0-9]*$/p'`" ] && echo string a is numbers

if grep &#39;^[[:digit:]]*$&#39; <<< "$1";then 
      echo "$1 is number." 
else 
      echo &#39;no.&#39; 
fi

if [ "$1" -gt 0 ] 2>/dev/null ;then 
      echo "$1 is number." 
else 
      echo 'no.' 
fi

case "$1" in 
  [1-9][0-9]*)  
    echo "$1 is number." 
    ;; 
  *)  
    ;; 
esac

echo $1| awk '{print($0~/^[-]?([0-9])+[.]?([0-9])+$/)?"number":"string"}'

if [ -n "$(echo $1| sed -n "/^[0-9]\+$/p")" ];then 
  echo "$1 is number." 
else 
  echo 'no.' 
fi

expr $1 "+" 10 &> /dev/null
if [ $? -eq 0 ];then
  echo "$1 is number"
else
  echo "$1 not number"
fi