linux shell实现转换输入日期的格式

#!/bin/sh
# normdate -- Normalizes month field in date specification
# to three letters, first letter capitalized. A helper
# function for Script #7, valid-date. Exits w/ zero if no error.

monthnoToName()
{
 # Sets the variable 'month' to the appropriate value
 case $1 in
  1 ) month="Jan"  ;; 2 ) month="Feb"  ;;
  3 ) month="Mar"  ;; 4 ) month="Apr"  ;;
  5 ) month="May"  ;; 6 ) month="Jun"  ;;
  7 ) month="Jul"  ;; 8 ) month="Aug"  ;;
  9 ) month="Sep"  ;; 10) month="Oct"  ;;
  11) month="Nov"  ;; 12) month="Dec"  ;;
  * ) echo "$0: Unknown numeric month value $1" >&2; exit 1
  esac
  return 0
}

## Begin main script

if [ $# -ne 3 ] ; then
 echo "Usage: $0 month day year" >&2
 echo "Typical input formats are August 3 1962 and 8 3 2002" >&2
 exit 1
fi

if [ $3 -lt 99 ] ; then
 echo "$0: expected four-digit year value." >&2; exit 1
fi

if [ -z $(echo $1|sed 's/[[:digit:]]//g') ]; then
 monthnoToName $1
else
 # Normalize to first three letters, first upper, rest lowercase
 month="$(echo $1|cut -c1|tr '[:lower:]' '[:upper:]')"
 month="$month$(echo $1|cut -c2-3 | tr '[:upper:]' '[:lower:]')"
fi

echo $month $2 $3

exit 0