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Full Discussion: head usage
Top Forums Shell Programming and Scripting head usage Post 302168262 by vasuarjula on Sunday 17th of February 2008 11:04:48 PM
Old 02-18-2008
head usage
Quote:
Originally Posted by qneill
A good debugging technique in most shells is to use "-x" which prints each command as it is executed. I put your commands in a script named 'yourscript'
Code:
bash$ cat yourscript                          # see the script
$ct=1
head -n $ct file

and then execute with -x:
Code:
bash$ bash -x yourscript                  # execute the script with -x
+ =1                                      # notice '$ct' is blank (you want 'ct')
script: line 1: =1: command not found     # which causes problems
+ head -n file                            # '$ct' is again blank
head: file: invalid number of lines       # more problems

Here's your corrected script (using 'ct=1')
Code:
bash$ cat yourscript 
ct=1
head -n $ct file
bash$ cat file
blah blah one
blah blah two
bash$ bash -x yourscript 
+ ct=1
+ head -n 1 file
blah blah one


sorry about that
my code is
ct=1
head -n $ct | tail -1
i will put this code in a while loop and increment ct.
so when ct =1 i will get the first record, when ct =2 then i will get the second record and so on....
But head -n $ct is not working. it says incorrect usage. Please let me know what is the problem
 

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LEARN ABOUT REDHAT

head

HEAD(1) 								FSF								   HEAD(1)

NAME

       head - output the first part of files

SYNOPSIS

       head [OPTION]... [FILE]...

DESCRIPTION

       Print  first  10 lines of each FILE to standard output.	With more than one FILE, precede each with a header giving the file name.  With no
       FILE, or when FILE is -, read standard input.

       Mandatory arguments to long options are mandatory for short options too.

       -c, --bytes=SIZE
	      print first SIZE bytes

       -n, --lines=NUMBER
	      print first NUMBER lines instead of first 10

       -q, --quiet, --silent
	      never print headers giving file names

       -v, --verbose
	      always print headers giving file names

       --help display this help and exit

       --version
	      output version information and exit

       SIZE may have a multiplier suffix: b for 512, k for 1K, m for 1 Meg.

AUTHOR

       Written by David MacKenzie.

REPORTING BUGS

       Report bugs to <bug-coreutils@gnu.org>.

COPYRIGHT

       Copyright (C) 2002 Free Software Foundation, Inc.
       This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU-
       LAR PURPOSE.

SEE ALSO

       The  full documentation for head is maintained as a Texinfo manual.  If the info and head programs are properly installed at your site, the
       command

	      info head

       should give you access to the complete manual.

head (coreutils) 4.5.3						   February 2003							   HEAD(1)
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