can't invoke sed properly...

[Laura Eaves]

Be careful putting the output into the same file as the input.
Note that I/O redirection takes place before the programs start running, so 
cat will open myfile and the shell will redirect the output to the input of 
sed, and before sed or cat ever start running, the shell will clobber the 
output file if it exists to make way for the output of sed.
Just use different names and later move the file back to the original if you 
want it updated.
Oh and you don't use the -e option -- I don't remember what version of sed I 
was using when I ran that.
But the -e option is useful if you have several patterns to apply to each 
input line.  sed will read the -e options left to right and treat each 
pattern as being on one line.  Of course you could always just use a quoted 
pattern that ran over multiple lines, but it is cleaner to use -e.

Finally, be careful using sed or any other pattern matching command, that 
you use single quotes instead of double quotes on the command line, as using 
double quotes will result in some undesired translation.  For example:

sed "1,$d"

will actually translate to

sed "1,xyz"

where xyz is the value of the environment variable d.
Lots of little gotchas in pattern matching.
Have fun!
--le

----- Original Message ----- 
From: "Lorenzo Taylor" <lorenzo at taylor.homelinux.net>
To: "Speakup is a screen review system for Linux." <speakup at braille.uwo.ca>
Sent: Monday, May 02, 2005 4:50 PM
Subject: Re: can't invoke sed properly...


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Someone tell me if there is an easier way, but this worked for me:

cat my-file | sed "s/red/blue/g" > my-file

This line replaced red with blue every time it appeared in the file.

I am using GNU sed version 4.1.4 here.  Your mileage may vary.

Lorenzo
- -- 
"We decided that we should evaluate the Microsoft offerings first. Once we
realised what a powerful set of tools they were, it became self-evident this 
was
the right way to go down."

Microsoft: the right way to go down
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