[NTLUG:Discuss] verify that a text string is a valid date.

[Leroy Tennison]

Chris Cox wrote:

>Richard Geoffrion wrote:
>  
>
>>I'm trying to do something but I don't know what it is called.
>>
>>I want to check to see if the first 10 characters of a file is a vaild 
>>date...eg  2006-02-01  and if it IS..then I want to continue the process.
>>
>>What am I trying to do in bash(or other utility terms)?  I don't know
>>the name of what I'm trying to do so I'm finding it difficult to search.
>>
>>    
>>
>
>$ mydate="2006-02-01"
>$ date -d "$mydate"
>Feb 28 00:00:00 CST 2006
>$ echo $?
>0
>$ mybaddate="2006-02-29"
>$ date -d "$mybaddate"
>date: invalid date `2006-02-29'
>$ echo $?
>1
>
>Is that enough to go on?  I can show a more
>programmatic example... sound like you know shell though.
>
>In true bourne shell fashion, I can pick off the
>first 10 characters of name like so (this would
>work with GNU date using Solaris's bourne shell):
>
>mydate=`expr "$name" : '\(..........\).*'`
>
>or with ksh... could use:
>
>mydate=${name%??????????}
>
>or with bash:
>
>mydate=${name:0:10}
>
>(there are many ways to do this obviously)
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>
>  
>
This has to be the most elegant solution I have seen (I was going to 
suggest awk but no need when an existing program can do all the tests 
for you).