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Top Forums Shell Programming and Scripting awk variables in regex expression ? Post 302486124 by michaelrozar17 on Friday 7th of January 2011 04:48:10 AM
Old 01-07-2011
Quote:
Originally Posted by vilius
Hello,

Could someone explain why this one returns nothing:
Code:
$ x=/jon/
$ echo jon | awk -v xa=$x '$1~xa {print}'
$

When a pattern matching is done using ~ we need to give the reg-exp in between / / (2 forward slashes).Still, when given inside the slashes it is taken as literally, so when changing the above awk as
Code:
echo jon | awk -v xa=$x '$1~/xa/ {print}'

it matches the word xa and not the variable xa's value.Hence we need to expand the variable as below
Code:
x=/jon/
echo jon | awk -v xa=$x '$1~/'"$xa"'/ {print}'

This is not the case when == is used as you would know this is used to equate between variables.Therefore in code $1==xa.. xa is expanded (to jon).
 

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OPENVT(1)							     Linux 1.x								 OPENVT(1)

NAME
openvt - start a program on a new virtual terminal (VT). SYNOPSIS
openvt [-c vtnumber] [-s] [-u] [-l] [-v] [--] command command_options DESCRIPTION
openvt will find the first available VT, and run on it the given command with the given command options, standard input, output and error are directed to that terminal. The current search path ($PATH) is used to find the requested command. If no command is specified then the environment variable $SHELL is used. OPTIONS -c vtnumber Use the given VT number and not the first available. Note you must have write access to the supplied VT for this to work. -e Directly execute the given command, without forking. This option is meant for use in /etc/inittab. -s Switch to the new VT when starting the command. The VT of the new command will be made the new current VT. -u Figure out the owner of the current VT, and run login as that user. Suitable to be called by init. Shouldn't be used with -c or -l. -l Make the command a login shell. A - is prepended to the name of the command to be executed. -v Be a bit more verbose. -w wait for command to complete. If -w and -s are used together then openvt will switch back to the controlling terminal when the com- mand completes. -- end of options to openvt. NOTE
If openvt is compiled with a POSIX (GNU) getopt() and you wish to set options to the command to be run, then you must supply the end of options -- flag before the command. EXAMPLES
openvt can be used to start a shell on the next free VT, by using the command: openvt bash To start the shell as a login shell, use: openvt -l bash To get a long listing you must supply the -- separator: openvt -- ls -l HISTORY
Earlier, openvt was called open. It was written by Jon Tombs <jon@gtex02.us.es or jon@robots.ox.ac.uk>. The -w idea is from "sam". SEE ALSO
chvt(1), doshell(8), login(1) 19 Jul 1996 V1.4 OPENVT(1)

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