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Full Discussion: <, >, >> and of course |
Top Forums UNIX for Dummies Questions & Answers <, >, >> and of course | Post 38923 by Perderabo on Wednesday 30th of July 2003 11:58:46 AM
Old 07-30-2003
Briefly,
> send the output to a file
>> appends the output to a file

So:
echo one > myfile
echo two >> myfile
results in two lines in myfile. While:
echo three > myfile
will result in one line in output file.

And if you what to view the file, one way would be:
cat < myfile
since < specifies an input file.

Think of the arrows as showing the flow of data.

There is a lot more to them, but this is a start.
 
replacekey(1)						      General Commands Manual						     replacekey(1)

NAME
replacekey - replace keywords in a FITS header SYNOPSIS
replacekey [options] <in> DESCRIPTION
replacekey is aimed at replacing keywords in a FITS file's header by new keywords provided by the user on the command-line. ALGORITHM
The user can provide a new_keyword, an old_keyword, a value and a comment. first searchs for old_keyword if provided. If it finds it, it replaces the associated card by the new one (new_keyword=value/comment). If old_keyword is either not found or not provided, associated card by the new one (new_keyword=value/comment). new_keyword has to be provided. Examples: You want to change the value of VALUE from 32 to 16 in myfile.fits: % replacekey -k "VALUE" -v "16" myfile.fits If you want to replace the card with the keyword OLD by "NEW = 3.14 / This is a usefull key" in myfile.fits: % replacekey -k "NEW" -v "3.14" -c "This is a usefull key" -K "OLD" myfile.fits If your do not care about the HISTORY cards you have in the header, and want to replace the first one by VALUE=32, you would do: % replacekey -k "VALUE" -v "32" -K "HISTORY" myfile.fits OPTIONS
-k or --key key To provide the new keyword. -K or --old key To provide the old keyword. -v or --val val To provide the new value. -c or --com com To provide the new comment. SEE ALSO
hierarch28 to convert HIERARCH ESO keywords to regular 8-char keywords. FILES
Files shall all comply with FITS format BUGS
Modifications are so far only possible in the main header, not in the extensions. 28 Oct 1999 replacekey(1)
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