printf的应用脚本

我们可以使用printf写个脚本，利用命令awk，要求输入一个日期，可以判断上个月的今天是什么时候。脚本如下：
#!/bin/awk
BEGIN {
print "input a date:[yyyymmdd]" ;
getline str;
len=length(str);
if ( len !=8 )
{
printf ("error str=%s,len=%d" , str,len );
exit
}

new_day=get_last_mon_day(str);

printf( "new-day is :%s\n" , new_day );
}
function get_last_mon_day (str)
{
vYear=strtonum(substr( str , 1 , 4 ));
vMonth=strtonum(substr( str , 5 , 2 ));
vDay=strtonum(substr( str , 7 , 2 ));

if ( vMonth == 1 )
{
vMonth=12;
vYear -= 1;
}
else
{
vMonth -= 1 ;
}

isLY=is_leap_year(vYear);

max_day=get_mon_day( isLY , vMonth );
if ( vDay > max_day )
vDay=max_day ;

new_day=sprintf( "%04d%02d%02d" , vYear , vMonth , vDay );
return new_day ;
}
function is_leap_year( vYear )
{
m4=vYear%4 ;
m100=vYear%100;
m400=vYear%400;

if ( m4 == 0 && m100 != 0 )
return 1 ;
if ( m400 == 0 )
return 1;
return 0;
}

function get_mon_day( isLY , vMonth )
{
#awk has no switch statement!!
if ( isLY == 0 )
astr="31,28,31,30,31,30,31,31,30,31,30,31";
else
astr="31,29,31,30,31,30,31,31,30,31,30,31";
split(astr,am,",");
return am[vMonth];
}

执行脚本：

awk -f get_date.sh