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Top Forums UNIX for Dummies Questions & Answers Help with changing header of tsv with 30 million lines Post 302747593 by binlib on Friday 21st of December 2012 05:21:07 PM
Old 12-21-2012
I will assume you want to change the header but keep the rest of the 30 million lines. Since the new header has the same length, the following will open file for both reading and writing:
Code:
sed -Ee '1s/s([1-4])/L\1/g' -e '1s/s([5-8])/W\1/g' -e '1y/5678/1234/' -e '1q' 0<file 1<>file

This will be very fast and replace the file in place. Be careful.
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UUENCODE(5)							File Formats Manual						       UUENCODE(5)

NAME
uuencode - format of an encoded uuencode file DESCRIPTION
Files output by uuencode(1) consist of a header line, followed by a number of body lines, and a trailer line. The uudecode(1) command will ignore any lines preceding the header or following the trailer. Lines preceding a header must not, of course, look like a header. The header line is distinguished by having the first 6 characters begin The word begin is followed by a mode (in octal), and a string which names the remote file. A space separates the three items in the header line. The body consists of a number of lines, each at most 62 characters long (including the trailing newline). These consist of a character count, followed by encoded characters, followed by a newline. The character count is a single printing character, and represents an inte- ger, the number of bytes the rest of the line represents. Such integers are always in the range from 0 to 63 and can be determined by sub- tracting the character space (octal 40) from the character. Groups of 3 bytes are stored in 4 characters, 6 bits per character. All are offset by a space to make the characters printing. The last line may be shorter than the normal 45 bytes. If the size is not a multiple of 3, this fact can be determined by the value of the count on the last line. Extra garbage will be included to make the character count a multiple of 4. The body is terminated by a line with a count of zero. This line consists of one ASCII space. The trailer line consists of end on a line by itself. SEE ALSO
uuencode(1), uudecode(1), uusend(1), uucp(1), mail(1) HISTORY
The uuencode file format appeared in BSD 4.0 . UUENCODE(5)
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