Re: IO Redirection

[Randall R Schulz <rrschulz at cris dot com>]

Robert,

[ Yes, Bjoern, this is OT for the Cygwin list as it's all about shell usage and not at all Cygwin specific. ]


You're using BASH, Robert. Except for the simple ">" and ">>" redirection, it's syntax is different from that of TCSH. Bjoern's answer was for TCSH.

I'm a BASH user, so I'll answer for that shell.

# Simple redirection of standard output only, overwriting existing file, if any:
% echo "foo is bar" >fbfile

# Appending redirection
% echo "foo is more bar" >>fbfile

# Redirect standard error only
% command-that-generates-error-output arg1 arg2 2>error-output

# Redirect standard output and standard error separately
% command arg >stdout 2>stderr

# Merge standard error with standard output
#   Order of redirection operators IS significant
% command arg1 arg2 >merged-output 2>&1


All the output redirections can be doubled for appending, but that does not apply to the descriptor merging forms (e.g., 2>&1, which means merge descriptor 2 with the current descriptor 1 and works for any number greater than 0).

Good luck. Get a good tutorial that covers BASH.

Randall Schulz
Mountain View, CA USA


At 02:54 2002-03-13, Robert Mark Bram wrote:
>Thanks for the reply!
>
>> > How do I append error output?
>> > How do I append error and standard output?
>>
>>  Just as you have written?
>>  ">>" appends, ">" write to a new file, independend of the file
>>  or source selected. That is,  "&>>file" appends both.
>>
>>  Why is that not obvious ?
>
>This is why:
>
>Robert Mark Bram@DIJONG ~
>$ ls
>errors  script1  script2  temp
>
>Robert Mark Bram@DIJONG ~
>$ ls &>> temp
>bash: syntax error near unexpected token `&>>'
>
>Robert Mark Bram@DIJONG ~
>$
>
>Rob


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