"awk variables in regex expression ?"

Post #302486124 by michaelrozar17 on Friday 7th of January 2011 03:48:10 AM

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).
 
UNIX and Linux Facts

Unix (trademarked as the UNIX certification mark) is a very mature family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix. Unix development starting in the 1970s by legendary Bell Labs programmers Ken Thompson, Dennis Ritchie, and others. Unix was first targetted for the Bell System and AT&T licensed Unix to outside parties. In the 1970s time period, this lead to a variety of for-profit as well as not-for-profit Unix variants. In the early days, this included the University of California, Berkeley (BSD), Microsoft (Xenix), IBM (AIX), and Sun Microsystems (Solaris). In the early 1990s AT&T sold their Unix rights to Novell. In 1995 Novell sold their Unix business to the Santa Cruz Operation (SCO). The UNIX trademark was passed to The Open Group, a "neutral" industry consortium. The Open Group promoted the use of the UNIX trademark for certified operating systems that comply with the Single UNIX Specification (SUS). In 2014 Apple's macOS became the Unix version with the largest global install base and macOS remains the largest Unix-user base today.
Linux is a family of open source Unix-like operating systems based on the Linux kernel. The Linux kernal is an operating system kernel first released by Linus Torvalds on 17 September 1991. Linux distributions include the Linux kernel, system software and libraries. Popular Linux distributions include Debian, Fedora, and Ubuntu. Commercial Linux distributions include Red Hat Enterprise Linux and SUSE Linux Enterprise Server. Linux is freely redistributable. Anyone may create a Linux distribution for any purpose.
Related Linux and UNIX Technical Support
Creating a regex expression
bigben1220
Good morning all!! In my code I and looking through file /etc/syslog.congf and printing every line that has /var/log in it. I need to turn the if 9$line) into a regex code instead. #!/usr/bin/perl @file= 'cat /etc/syslog.conf'; //when foreach $line (@file){ if ($line =~...... Shell Programming and Scripting
3
Shell Programming and Scripting
help with simple regex expression
schms
I am trying to grep the following line in a file using a bash shell: (..) admin1::14959:::::: (..) It works with the following expression (as expected) # cat file | grep ^*:: admin1::14959:::::: but it does not work with (not expected) # cat /etc/shadow | grep ^+:: I assume the...... Shell Programming and Scripting
2
Shell Programming and Scripting
passing a regex as variable to awk and using that as regular expression for search
k_bijitesh
Hi All, I have a sftp session log where I am transferring multi files by issuing "mput abc*.dat". The contents of the logfile is below - ################################################# Connecting to 10.75.112.194... Changing to: /home/dasd9x/testing1 sftp> mput abc*.dat Uploading...... Shell Programming and Scripting
7
Shell Programming and Scripting
awk regex expression works in AIX but not in Linux
kamlesh_pradhan
I have following expression: echo "Sun 12 Jul BST 2014\nSun 12 Jul 2014\nSun 12 Jul IS 2014" | awk '/(Sun)+( 12)+( Jul )+({3} )?(2014)/{print;}' I ran above code in AIX box and output is as follows Sun 12 Jul BST 2014 Sun 12 Jul 2014 I ran above code in Linux box and output is as...... Shell Programming and Scripting
8
Shell Programming and Scripting
Regex Expression Replace
dr46014
I have a XML file where there is a tag with like <wd:address_line_1>1234 Street</wd:address_line_1> I want to replace the values "1234 Street" with "Test Data". Different people have different address lines and i want to replace with a fixed value to mask the file. I was trying to use sed...... UNIX for Beginners Questions & Answers
7
UNIX for Beginners Questions & Answers