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Full Discussion: How to read a file starting at certain line number?
Top Forums Shell Programming and Scripting How to read a file starting at certain line number? Post 302950973 by wisecracker on Thursday 30th of July 2015 05:30:56 PM
Old 07-30-2015
Longhand using builtins only and has a start and finish to select any or all lines.
If you have no idea how many lines there are then just give $2 a rediculously large value, say 1000000...
OSX 10.7.5, default bash terminal.
Code:
#!/bin/bash
# line_no
# Usage: line_no start finish /full/path/to/filename /full/path/to/outfile
# Note:- There is no user error correction code here so don't make any typos.
ifs_str="$IFS"
IFS=$'\n'
# Working part.
n=1
while read -r line
do
	if [ $n -ge $1 ] && [ $n -le $2 ]
	then
		echo -E $line
	fi
	n=$(($n+1))
done < $3 > $4
# End of working part.
cat $4
IFS="$ifs_str"
exit

Results...
Code:
Last login: Thu Jul 30 22:11:35 on ttys000
AMIGA:barrywalker~> cd Desktop/Code/Shell
AMIGA:barrywalker~/Desktop/Code/Shell> ./line_no 1 1 ~/AudioScope.sh /tmp/text
#!/bin/bash
AMIGA:barrywalker~/Desktop/Code/Shell> ./line_no 3470 3489 ~/AudioScope.sh /tmp/text
#               |        /    --+--     /         | +     /      ------------
#               |     R1 \     / \ D1   \ R2     === C2   \ R3
#               |        /    '---'     /        -+-      /
#               |        \      |       \         |       \ 
#               |        /      |       /         o       /
#               |        |      |       |         |       |       Y
#               +--------o------o-------o---------o---o---o-------O -VE.
#                              Pseudo Ground. ----> __|__
#                                             _GND_ /////
# Parts List:-
# C1 ......... 1 uF, 50V.
# C2 ......... 10 uF, electrolytic, 10V, IMPORTANT! SEE TEXT.
# R1 ......... 33R, 1/8W, 5% tolerance resistor.
# R2 ......... 1M, 1/8W, 5% tolerance resistor.
# R3 ......... 100K, 1/8W, 5% tolerance resistor.
# D1, D2 ..... OA90 or any similar germanium diode.
# 3.2mm standard STEREO jack plug for headset socket.
# Coaxial connecting cable.
# Sundries as required, stripboard, etc, (similar to above).
# #########################################################
AMIGA:barrywalker~/Desktop/Code/Shell> _

EDIT:
Hmm, just thought my Android phone does not have commands like 'tail', etc, so this could be useful...
Decided to remove variable names and use $1, $2, $3 and $4 directly instead.
Last edited by wisecracker; 07-31-2015 at 04:15 AM.. Reason: See above.
 

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LEARN ABOUT MOJAVE

gets

gets(n) 						       Tcl Built-In Commands							   gets(n)

__________________________________________________________________________________________________________________________________________________

NAME

       gets - Read a line from a channel

SYNOPSIS

       gets channelId ?varName?
_________________________________________________________________

DESCRIPTION

       This command reads the next line from channelId, returns everything in the line up to (but not including) the end-of-line character(s), and
       discards the end-of-line character(s).

       ChannelId must be an identifier for an open channel such as the Tcl standard input channel (stdin), the return value from an invocation	of
       open or socket, or the result of a channel creation command provided by a Tcl extension. The channel must have been opened for input.

       If  varName  is omitted the line is returned as the result of the command.  If varName is specified then the line is placed in the variable
       by that name and the return value is a count of the number of characters returned.

       If end of file occurs while scanning for an end of line, the command returns whatever input is available up to the end of file.	 If  chan-
       nelId  is in nonblocking mode and there is not a full line of input available, the command returns an empty string and does not consume any
       input.  If varName is specified and an empty string is returned in varName because of end-of-file or because of insufficient data  in  non-
       blocking  mode,	then  the return count is -1.  Note that if varName is not specified then the end-of-file and no-full-line-available cases
       can produce the same results as if there were an input line consisting only of the end-of-line character(s).  The eof and fblocked commands
       can be used to distinguish these three cases.

EXAMPLE

       This example reads a file one line at a time and prints it out with the current line number attached to the start of each line.

	      set chan [open "some.file.txt"]
	      set lineNumber 0
	      while {[gets $chan line] >= 0} {
		  puts "[incr lineNumber]: $line"
	      }
	      close $chan

SEE ALSO

       file(n), eof(n), fblocked(n), Tcl_StandardChannels(3)

KEYWORDS

       blocking, channel, end of file, end of line, line, nonblocking, read

Tcl									7.5								   gets(n)
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