Best performance to merge two files


 
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# 8  
Old 12-14-2018
Quote:
Originally Posted by green_k
Hi Gurus,


I need to merge two files.


file1 (small file, only one line)
Code:
this is first line

file2 (large file)
Code:
 abc
def
ghi
...

I use below command to merge the file, since the file2 is really large file, the command read whole file2, the performance is not good.
Code:
cat file1 > file3
cat file2 >> file2

I searched internet, there is suggestion to use
Code:
sed -i '1 i\anything' file or 
sed -i '1i text' filename

the command thrown out error
Code:
sed: illegal option -- i

please provide your valuable suggestion.

my os is SunOS 5.10 Generic_150400-04 sun4v sparc sun4v


thanks in advance
Note that the command vgersj99 suggested in post #4 is logically equivalent to the commands:
Code:
cat file1 > file3
cat file2 >> file3

but runs a little bit faster because it only needs to invoke cat once instead of twice.

This is very different from the code you tried that I marked in red above. You said the performance of that code was not good. The second line of that code:
Code:
cat file2 >> file2

is an infinite loop copying the initial contents of the file named file2 to the end of itself and continuing copying until you hit the maximum size allowed by your operating system for you to create, the file system containing file2 fills up, or you terminate the cat. One might assume that the last line of that was a typo and what you intended was:
Code:
cat file2 >> file3

but if what you showed us really is what you had, the time taken to filll up a file system might be mistaken for poor performance.
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