UNIX for Dummies Questions & Answers

HI ,

I am having a huge comma delimiter file, I have to append the following four lines before the starting of the file through a shell script.

FILE NAME = TEST_LOAD
DATETIME = CURRENT DATE TIME
LOAD DATE = CURRENT DATE
RECORD COUNT = TOTAL RECORDS IN FILE

Code:

Source data

1,2,3,4,5,6,7
8,9,1,2,3,4,5

Code:

Target Data

FILE NAME = TEST_LOAD
DATETIME = 220820110812
LOAD DATE = 22082011
RECORD COUNT = 2
1,2,3,4,5,6,7
8,9,1,2,3,4,5

Using the awk NR I can get the record counts, but I am not sure how to insert the headers and the record count at the starting of the file, as the file is huge i don't want to copy the file and make the changes.

is there any way by which i can add the four lines which out duplicating the file.

Please suggest.

Regards,
Shruthi

No way. You have to make a new copy of the file explicitly or implicitly (perl or GNU sed with -i option).

HI ,

I tried the below code but it's giving the error at the datetime part.

Code:

awk 'BEGIN { print "file_name = test_count" }  print { Datetime = "date +%Y%m%d%H%M%S"} print {date = "date"} print {record_count = NR} { print $0 }'  test.csv > test_gen.csv

can you pls tell where I am doing it wrong.

Regards,
Shruthi

You don't need awk. Do something like this:

Code:

echo 'file_name = test_count' >new
date >>new
wc -l original_file >>new
cat original_file >> new

That's incorrect. ed can be used to modify a file without creating another file in the filesystem.

The following may give the original poster some ideas:

Code:

filename=data
ed -s "$filename" <<EOED
1i
FILENAME = $filename
DATETIME = $(date +%Y%m%d%H%M%S)
RECORD_COUNT = $(awk 'END {print NR}' "$filename")
.
w
q
EOED

Caveat: It's never been a problem for me, but keep in mind that ed uses a single dot on a line by itself to delimit the data being inserted. Should the inserted data itself contain a dot by itself on a line, it would need to be protected with an unambiguous decoration. After the insertion, the substitute command can be used to undecorate.

Yes. You can use ed or any editor or write a very simple program to read a file in memory, delete a file and write the new one. But "the file is huge" and ed should make some copy or use a virtual memory or something like. I don't know may be it's possible to play somehow with inodes to add bytes to the start of file but I didn't hear about it.

yazu is correct, there's no trivial way to add bytes to the front of a file. Any method would involve the same thing, generating a new file with the right bytes in the front.