http://stackoverflow.com/questions/6762348/what-do-and-do-in-tcsh 写道
In tcsh redirection the ! symbol means overwrite the existing file even if noclobber is set.
In other words, if noclobber is set then:
cmd > file will write stdout to file if file does not exist
cmd > file will fail if file exists
cmd >> file will append stdout to file if file exists
cmd >> file will fail if file does not exist
cmd >! file will write stdout to file, overwriting any existing file
cmd >>! file will append stdout to file, creating the file if it does not already exist
If noclobber is not set then the ! has no effect:
cmd > file will write stdout to file, overwriting any existing file
cmd >> file will append stdout to file
cmd >! file will write stdout to file, overwriting any existing file
cmd >>! file will append stdout to file
In other words, if noclobber is set then:
cmd > file will write stdout to file if file does not exist
cmd > file will fail if file exists
cmd >> file will append stdout to file if file exists
cmd >> file will fail if file does not exist
cmd >! file will write stdout to file, overwriting any existing file
cmd >>! file will append stdout to file, creating the file if it does not already exist
If noclobber is not set then the ! has no effect:
cmd > file will write stdout to file, overwriting any existing file
cmd >> file will append stdout to file
cmd >! file will write stdout to file, overwriting any existing file
cmd >>! file will append stdout to file
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