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Top Forums UNIX for Dummies Questions & Answers extracting selected few lines through perl Post 302213264 by tinivole on Wednesday 9th of July 2008 05:28:51 PM
Old 07-09-2008
a2p and s2p

Hi, so far as I know, there isn't any truly easy way to do this in Perl in quite the same way that awk and sed provides.

But there are two Perl apps that will convert awk and sed code into Perl for you, so you can perhaps learn from them instead.

The first being a2p (awk to perl) and the second being s2p (sed to perl)

To answer one of your example questions, you can emulate "head" in sed with the command:
Code:
sed 10q

So, to convert that into Perl code and save it to a file for reading. The command:
Code:
s2p 10q > head.pl

Would acheive that.

Although, I did say that there isn't any truly easy way in Perl, and you may be quite blown by the output of that command.

Regards
Iain
 

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TAIL(1) 						    BSD General Commands Manual 						   TAIL(1)

NAME
tail -- display the last part of a file SYNOPSIS
tail [-F | -f | -r] [-q] [-b number | -c number | -n number] [file ...] DESCRIPTION
The tail utility displays the contents of file or, by default, its standard input, to the standard output. The display begins at a byte, line or 512-byte block location in the input. Numbers having a leading plus ('+') sign are relative to the beginning of the input, for example, ``-c +2'' starts the display at the second byte of the input. Numbers having a leading minus ('-') sign or no explicit sign are relative to the end of the input, for example, ``-n 2'' displays the last two lines of the input. The default start- ing location is ``-n 10'', or the last 10 lines of the input. The options are as follows: -b number The location is number 512-byte blocks. -c number The location is number bytes. -f The -f option causes tail to not stop when end of file is reached, but rather to wait for additional data to be appended to the input. The -f option is ignored if the standard input is a pipe, but not if it is a FIFO. -F The -F option implies the -f option, but tail will also check to see if the file being followed has been renamed or rotated. The file is closed and reopened when tail detects that the filename being read from has a new inode number. If the file being followed does not (yet) exist or if it is removed, tail will keep looking and will display the file from the begin- ning if and when it is created. The -F option is the same as the -f option if reading from standard input rather than a file. -n number The location is number lines. -q Suppresses printing of headers when multiple files are being examined. -r The -r option causes the input to be displayed in reverse order, by line. Additionally, this option changes the meaning of the -b, -c and -n options. When the -r option is specified, these options specify the number of bytes, lines or 512-byte blocks to display, instead of the bytes, lines or blocks from the beginning or end of the input from which to begin the display. The default for the -r option is to display all of the input. If more than a single file is specified, each file is preceded by a header consisting of the string ``==> XXX <=='' where XXX is the name of the file unless -q flag is specified. EXIT STATUS
The tail utility exits 0 on success, and >0 if an error occurs. EXAMPLES
To display the last 500 lines of the file foo: $ tail -n 500 foo Keep /var/log/messages open, displaying to the standard output anything appended to the file: $ tail -f /var/log/messages SEE ALSO
cat(1), head(1), sed(1) STANDARDS
The tail utility is expected to be a superset of the IEEE Std 1003.2-1992 (``POSIX.2'') specification. In particular, the -F, -b and -r options are extensions to that standard. The historic command line syntax of tail is supported by this implementation. The only difference between this implementation and historic versions of tail, once the command line syntax translation has been done, is that the -b, -c and -n options modify the -r option, i.e., ``-r -c 4'' displays the last 4 characters of the last line of the input, while the historic tail (using the historic syntax ``-4cr'') would ignore the -c option and display the last 4 lines of the input. HISTORY
A tail command appeared in PWB UNIX. BSD
March 16, 2013 BSD
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