Shell Programming and Scripting

I have a 1.2G file that contains no newline characters. This is essentially a log file with each entry being exactly 78bits long. The basic format is /DATE/USER/MISC/. The single uniform thing about the file is that that the 8 character is always ":"

I worked with smaller files of the same data before using the following command

Code:

 ggrep -E -o ".{0,8}\:.{0,67}" LOG.txt

but the problem with this particular file is the size of the file itself. At 1.2G ggrep runs out of memory....

Code:

ggrep: memory exhausted

looking for a way to break up the file or get around the memory limits.

Having an entry that is 78 bits long that contains characters is very strange. Most entries in a file are a stream of 8 bit bytes. So, to split your entries (each of which is 9.75 bytes) into 11 byte lines (your 9.75 bytes per entry plus 2 bits for byte packing and a newline so the output is a text file), you're probably going to find writing a C program to read bytes and rotate bits into the proper positions easier than doing it in a shell script.

What two bits should be added to your entries to produce 10 characters (assuming ASCII or EBCDIC) from your input entries?

If your entries are all 78 bits long, why is your grep looking for a varying number of characters before and after the colon and why is the string it is matching varying from 1 to 76 characters (not bits or bytes) inclusive instead of the 78 bits you specified???

Please show us the first 200 bytes of your input file piped through the command:

Code:

od -bcx

Looking at the example I think OP meant 78 bytes

If exists on your system, would

Code:

fold -w78 file

work?

If the records are all of fixed size, dd can be used to insert a newline after them. An example with 4 byte fixed size records:

Code:

# bs is 1 minus the record size, cbs is the record size.
$ printf "AAA:BBB:CCC:DDD:" | dd bs=3 cbs=4 conv=unblock

AAA:
BBB:
CCC:
DDD:

$

dd is unaffected by line length limitations. You chould chain this before an awk or grep or what have you.

Code:

dd if=filename ... | grep whatever

I assume you meant bs=4 instead of bs=3, but when processing a 1.2Gb file, dd will run noticeably faster with its default block size (512 bytes) or a larger size like bs=1024000. The dd bs=n parameter specifies how many bytes dd will read at a time from its input file and how many bytes at a time it will write to its output file.

With conv=unblock, it is just the conversion buffer size (specified by cbs=n) that determines the output line length produced by the dd utility.

No, I meant bs=3. That is what it seemed to require from empirical testing.

You are correct. It appeared to require it but that was my mistake (probably from still using the sync option at the time).

You might even do bs=4M.