[ale] Another Large File/PERL/Awk/Sed question...

[JK]

Richard Bronosky wrote:
> in sed, use '[range/line number]{commands}' to limit where the edits
> are made. Example:
> mount |sed '1{s/type/TEST/}'
> 
> what you want is:
> sed -i.bak '1{s/column4/column5/}' filename


Interesting...

For single commands, address-space-command also works, so:

   sed -i -e '1 s/column4;column4/column4;column5/'

would work as well as the {} version.  My previous attempt
was wrong though, in that 0 is not a valid address in at
least some versions of sed. In fact, the man page for 4.2.1
says 0 IS valid, and means "really for sure start matching
at the very first line" (there are some circumstances where
1 will NOT match, to wit, if line 1 matches the regexp
specified as the ending address); but 4.2.1 does not actually
accept that syntax.

-- JK



> A backup filename.bak will be created with that command. drop the
> -i.bak if you don't want it.
> 
> 
> On Tue, Dec 1, 2009 at 4:06 PM, Bob Kruger <bkruger at mindspring.com> wrote:
>> All;
>>
>> Thanks to all who assisted me with my earlier question on deleting the semicolon from the end of a line.  I have another one that may be a bit stickier.
>>
>> Again I have a large data file in text format, this one is 3.2GB.  Same as before, the field are semicolon delimited.  The first line of the file is the column name.  However, I have two columns that were inadvertently given the same column name.
>>
>> Example:
>>
>> column1;column2;column3;column4;column4;column6;column7....
>>
>> I would like to change the second instance of column4 to column5 on the first line of the file.  I thought it would be simple to fire up vi and just do a simple text edit.  The edit part was simple, but the saving of the file is taking hours.
>>
>> Any thoughts or ideas using PERL, Awk, or Sed?
>>
>> Thanks in advance for any assistance.
>>
>> V/r
>>
>> Bob
>>
>>
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> 
>