select a record from one file matching from second file using awk Post: 302204323

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Top Forums Shell Programming and Scripting select a record from one file matching from second file using awk Post 302204323 by synmag on Wednesday 11th of June 2008 09:49:44 AM

06-11-2008

Registered User

Quote:

Originally Posted by era

Oh, I misunderstood your problem description. Here's something which hopefully is closer to what you wanted.

Code:

awk -F , -v acct=root 'NR==FNR { h[$1]++; next; }
{ if($1 == "") $1=host; host=$1; if (! h[$1]) next;
if ($2 == acct) print }' fileb filea

The NR==FNR condition is true while fileb is being read. This is a common awk idiom for reading in a file of auxiliary data before the main processing. The host names in fileb will be used to populate the array h. Then in the main body of the script, if the first field is empty, the value of the host variable will be used for $1. Then the current value of $1 will be remembered in host in case the next line(s) have empty first fields. Then, if the array h does not contain the current host name (meaning it was not present in fileb), the current line is skipped. Finally, if the second field is identical to the variable acct, the line is printed.

(Really old variants of awk do not support passing in variables with the -v option -- if you have this problem, see if you can find nawk or mawk or gawk on your system, or an XPG4 awk. Or you can interpolate the variable directly into the script.)

That's exactly what I wanted. My version of awk didn't support the passing of the variable but I do have nawk and it worked perfectly.

Based on awk documentation I was trying to use the begin block to read the file but couldn't figure out how to read from two files. Would you mind explaining how awk determines which file to read from? Is it the code in the first set of braces {} reads the first file supplied and the second set the second file?

Thank you. I learned a lot from this!

synmag

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qmail-popup

qmail-popup(8)						      System Manager's Manual						    qmail-popup(8)

NAME

       qmail-popup - read a POP username and password

SYNOPSIS

       qmail-popup hostname subprogram

DESCRIPTION

       qmail-popup reads a POP username and password from the network.	It then runs subprogram.

       qmail-popup is most commonly invoked from inetd as

	  qmail-popup CHANGEME checkpassword qmail-pop3d Maildir

       with CHANGEME replaced by the fully qualified domain name of the local host.

       qmail-popup  expects descriptor 0 to read from the network and descriptor 1 to write to the network.  It reads a username and password from
       descriptor 0 in POP's USER-PASS style or APOP style.  It invokes subprogram, with the same descriptors 0 and 1; descriptor 2 writing to the
       network;  and  descriptor  3  reading  the username, a 0 byte, the password, another 0 byte, an APOP timestamp derived from hostname, and a
       final 0 byte.  qmail-popup then waits for subprogram to finish.	It prints an error message if subprogram crashes or exits nonzero.

       qmail-popup should be used only within a secure network.  Otherwise an eavesdropper can steal passwords.  Even if you use APOP,	an  active
       attacker can still take over the connection and wreak havoc.

       qmail-popup has a 20-minute idle timeout.

       qmail-popup is based on a program contributed by Russ Nelson.

SEE ALSO

       maildir(5), qmail-local(8), qmail-pop3d(8)

																    qmail-popup(8)