[2012-07-13]趣味习题：获取最近一百年内的所有黑色星期五的日期

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今天是2012-07-13 星期五，所以刚好有了这么个想法，获取最近100年的所有黑色星期五的日子。
丢个砖：

personball@vostro:SHELL$cat GetBlackFri.sh
#!/bin/bash
first="2012-07-13 00:00:00"
tst=`date -d "$first" "+%s"`
for i in {1..5200}
do
    let "tst=tst-86400*7"
    str=` date -d "@$tst" `
    if [[ "$str" =~ " 13 " ]]
    then
        echo $str
    fi
done
personball@vostro:SHELL$./GetBlackFri.sh
Fri Apr 13 00:00:00 CST 2012
Fri Jan 13 00:00:00 CST 2012
Fri May 13 00:00:00 CST 2011
Fri Aug 13 00:00:00 CST 2010
Fri Nov 13 00:00:00 CST 2009
Fri Mar 13 00:00:00 CST 2009
Fri Feb 13 00:00:00 CST 2009
Fri Jun 13 00:00:00 CST 2008
Fri Jul 13 00:00:00 CST 2007
Fri Apr 13 00:00:00 CST 2007
Fri Oct 13 00:00:00 CST 2006
Fri Jan 13 00:00:00 CST 2006
Fri May 13 00:00:00 CST 2005
Fri Aug 13 00:00:00 CST 2004
Fri Feb 13 00:00:00 CST 2004
Fri Jun 13 00:00:00 CST 2003
Fri Dec 13 00:00:00 CST 2002
Fri Sep 13 00:00:00 CST 2002
Fri Jul 13 00:00:00 CST 2001
Fri Apr 13 00:00:00 CST 2001
Fri Oct 13 00:00:00 CST 2000
Fri Aug 13 00:00:00 CST 1999
Fri Nov 13 00:00:00 CST 1998
Fri Mar 13 00:00:00 CST 1998
Fri Feb 13 00:00:00 CST 1998
Fri Jun 13 00:00:00 CST 1997
Fri Dec 13 00:00:00 CST 1996
Fri Sep 13 00:00:00 CST 1996
Fri Oct 13 00:00:00 CST 1995
Fri Jan 13 00:00:00 CST 1995
Fri May 13 00:00:00 CST 1994
Fri Aug 13 00:00:00 CST 1993
Fri Nov 13 00:00:00 CST 1992
Fri Mar 13 00:00:00 CST 1992
Fri Dec 13 00:00:00 CST 1991
Fri Sep 13 01:00:00 CDT 1991
Fri Jul 13 01:00:00 CDT 1990
Fri Apr 13 00:00:00 CST 1990
Fri Oct 13 00:00:00 CST 1989
Fri Jan 13 00:00:00 CST 1989
Fri May 13 01:00:00 CDT 1988
Fri Nov 13 00:00:00 CST 1987
Fri Mar 13 00:00:00 CST 1987
Fri Feb 13 00:00:00 CST 1987
Fri Jun 13 01:00:00 CDT 1986
Fri Dec 13 00:00:00 CST 1985
Fri Sep 13 00:00:00 CST 1985
Fri Jul 13 00:00:00 CST 1984
Fri Apr 13 00:00:00 CST 1984
Fri Jan 13 00:00:00 CST 1984
Fri May 13 00:00:00 CST 1983
Fri Aug 13 00:00:00 CST 1982
Fri Nov 13 00:00:00 CST 1981
Fri Mar 13 00:00:00 CST 1981
Fri Feb 13 00:00:00 CST 1981
Fri Jun 13 00:00:00 CST 1980
Fri Jul 13 00:00:00 CST 1979
Fri Apr 13 00:00:00 CST 1979
Fri Oct 13 00:00:00 CST 1978
Fri Jan 13 00:00:00 CST 1978
Fri May 13 00:00:00 CST 1977
Fri Aug 13 00:00:00 CST 1976
Fri Feb 13 00:00:00 CST 1976
Fri Jun 13 00:00:00 CST 1975
Fri Dec 13 00:00:00 CST 1974
Fri Sep 13 00:00:00 CST 1974
Fri Jul 13 00:00:00 CST 1973
Fri Apr 13 00:00:00 CST 1973
Fri Oct 13 00:00:00 CST 1972
Fri Aug 13 00:00:00 CST 1971
Fri Nov 13 00:00:00 CST 1970
Fri Mar 13 00:00:00 CST 1970
Fri Feb 13 00:00:00 CST 1970
Fri Jun 13 00:00:00 CST 1969
Fri Dec 13 00:00:00 CST 1968
Fri Sep 13 00:00:00 CST 1968
Fri Oct 13 00:00:00 CST 1967
Fri Jan 13 00:00:00 CST 1967
Fri May 13 00:00:00 CST 1966
Fri Aug 13 00:00:00 CST 1965
Fri Nov 13 00:00:00 CST 1964
Fri Mar 13 00:00:00 CST 1964
Fri Dec 13 00:00:00 CST 1963
Fri Sep 13 00:00:00 CST 1963
Fri Jul 13 00:00:00 CST 1962
Fri Apr 13 00:00:00 CST 1962
Fri Oct 13 00:00:00 CST 1961
Fri Jan 13 00:00:00 CST 1961
Fri May 13 00:00:00 CST 1960
Fri Nov 13 00:00:00 CST 1959
Fri Mar 13 00:00:00 CST 1959
Fri Feb 13 00:00:00 CST 1959
Fri Jun 13 00:00:00 CST 1958
Fri Dec 13 00:00:00 CST 1957
Fri Sep 13 00:00:00 CST 1957
Fri Jul 13 00:00:00 CST 1956
Fri Apr 13 00:00:00 CST 1956
Fri Jan 13 00:00:00 CST 1956
Fri May 13 00:00:00 CST 1955
Fri Aug 13 00:00:00 CST 1954
Fri Nov 13 00:00:00 CST 1953
Fri Mar 13 00:00:00 CST 1953
Fri Feb 13 00:00:00 CST 1953
Fri Jun 13 00:00:00 CST 1952
Fri Jul 13 00:00:00 CST 1951
Fri Apr 13 00:00:00 CST 1951
Fri Oct 13 00:00:00 CST 1950
Fri Jan 13 00:00:00 CST 1950
Fri May 13 00:00:00 CST 1949
Fri Aug 13 00:00:00 CST 1948
Fri Feb 13 00:00:00 CST 1948
Fri Jun 13 00:00:00 CST 1947
Fri Dec 13 00:00:00 CST 1946
Fri Sep 13 00:00:00 CST 1946
Fri Jul 13 00:00:00 CST 1945
Fri Apr 13 00:00:00 CST 1945
Fri Oct 13 00:00:00 CST 1944
Fri Aug 13 00:00:00 CST 1943
Fri Nov 13 00:00:00 CST 1942
Fri Mar 13 00:00:00 CST 1942
Fri Feb 13 00:00:00 CST 1942
Fri Jun 13 01:00:00 CDT 1941
Fri Dec 13 00:00:00 CST 1940
Fri Sep 13 01:00:00 CDT 1940
Fri Oct 13 00:00:00 CST 1939
Fri Jan 13 00:00:00 CST 1939
Fri May 13 00:00:00 CST 1938
Fri Aug 13 00:00:00 CST 1937
Fri Nov 13 00:00:00 CST 1936
Fri Mar 13 00:00:00 CST 1936
Fri Dec 13 00:00:00 CST 1935
Fri Sep 13 00:00:00 CST 1935
Fri Jul 13 00:00:00 CST 1934
Fri Apr 13 00:00:00 CST 1934
Fri Oct 13 00:00:00 CST 1933
Fri Jan 13 00:00:00 CST 1933
Fri May 13 00:00:00 CST 1932
Fri Nov 13 00:00:00 CST 1931
Fri Mar 13 00:00:00 CST 1931
Fri Feb 13 00:00:00 CST 1931
Fri Jun 13 00:00:00 CST 1930
Fri Dec 13 00:00:00 CST 1929
Fri Sep 13 00:00:00 CST 1929
Fri Jul 13 00:00:00 CST 1928
Fri Apr 13 00:00:00 CST 1928
Fri Jan 13 00:00:00 CST 1928
Fri May 13 00:05:52 LMT 1927
Fri Aug 13 00:05:52 LMT 1926
Fri Nov 13 00:05:52 LMT 1925
Fri Mar 13 00:05:52 LMT 1925
Fri Feb 13 00:05:52 LMT 1925
Fri Jun 13 00:05:52 LMT 1924
Fri Jul 13 00:05:52 LMT 1923
Fri Apr 13 00:05:52 LMT 1923
Fri Oct 13 00:05:52 LMT 1922
Fri Jan 13 00:05:52 LMT 1922
Fri May 13 00:05:52 LMT 1921
Fri Aug 13 00:05:52 LMT 1920
Fri Feb 13 00:05:52 LMT 1920
Fri Jun 13 00:05:52 LMT 1919
Fri Dec 13 00:05:52 LMT 1918
Fri Sep 13 00:05:52 LMT 1918
Fri Jul 13 00:05:52 LMT 1917
Fri Apr 13 00:05:52 LMT 1917
Fri Oct 13 00:05:52 LMT 1916
Fri Aug 13 00:05:52 LMT 1915
Fri Nov 13 00:05:52 LMT 1914
Fri Mar 13 00:05:52 LMT 1914
Fri Feb 13 00:05:52 LMT 1914
Fri Jun 13 00:05:52 LMT 1913
Fri Dec 13 00:05:52 LMT 1912

有没注意到输出中有几个异常时间点？
注意初始值是从今天0点0分0秒开始算的，每次循环减去7天的秒数。
出现了以下几个时间点：

Fri Sep 13 01:00:00 CDT 1991
Fri Jul 13 01:00:00 CDT 1990
Fri May 13 01:00:00 CDT 1988
Fri Jun 13 01:00:00 CDT 1986
Fri Jun 13 01:00:00 CDT 1941
Fri Sep 13 01:00:00 CDT 1940
Fri May 13 00:05:52 LMT 1927
Fri Aug 13 00:05:52 LMT 1926
Fri Nov 13 00:05:52 LMT 1925
Fri Mar 13 00:05:52 LMT 1925
Fri Feb 13 00:05:52 LMT 1925
Fri Jun 13 00:05:52 LMT 1924
Fri Jul 13 00:05:52 LMT 1923
Fri Apr 13 00:05:52 LMT 1923
Fri Oct 13 00:05:52 LMT 1922
Fri Jan 13 00:05:52 LMT 1922
Fri May 13 00:05:52 LMT 1921
Fri Aug 13 00:05:52 LMT 1920
Fri Feb 13 00:05:52 LMT 1920
Fri Jun 13 00:05:52 LMT 1919
Fri Dec 13 00:05:52 LMT 1918
Fri Sep 13 00:05:52 LMT 1918
Fri Jul 13 00:05:52 LMT 1917
Fri Apr 13 00:05:52 LMT 1917
Fri Oct 13 00:05:52 LMT 1916
Fri Aug 13 00:05:52 LMT 1915
Fri Nov 13 00:05:52 LMT 1914
Fri Mar 13 00:05:52 LMT 1914
Fri Feb 13 00:05:52 LMT 1914
Fri Jun 13 00:05:52 LMT 1913
Fri Dec 13 00:05:52 LMT 1912

百度百科
CST

CST同时代表了下面4个时区：
CST：Central Standard Time (USA) 中部标准时间(美国) UTC -6:00
CST：Central Standard Time (Australia) 中部标准时间(澳大利亚) UTC 9:30
CST：China Standard Time 中国标准时间(北京时间) UTC 8:00
CST： Cuba Standard Time 古巴标准时间 UTC -4:00

注：UTC：协调世界时，又称世界标准时间或世界协调时间，简称UTC，从英文“Coordinated Universal Time” 称为世界统一时间。

同时还有相关：

EDT - Eastern Daylight Time 东部夏令时间

CDT

CDT - Central Daylight Time 中部夏令时间

LMT

LMT（local mean time）地方平时
LMT又称地方时。平太阳中心经过测者子圈后所经历的时间。因地方平时是从平太阳中心经过测者子圈起算的，在同一时刻不同经线上的地方平时不相等。故地方平时在日常生活中使用不便，只适用于天文测量等方面。

最后，关于时间还有个历法上的事情：wiki儒略历