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Old 10-14-2006, 05:36 PM   #1
pete1234
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Distribution: Slack, FreeBSD,NetBSD, OpenBSD, Open Solaris, Minix
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awk code explanation


This awk code is suppose to remove the username and all fields related to that user:

Code:
nawk -v name='1testone' -f kang.awk myFile.txt
/^[^ ]/ { found= ($1 == name) ? 1 : 0 }
!found
Here's the file:

Code:
testone          Password = "11111"
                    Service-Type = "Framed-User",
                    Session-Timeout = "9000",
                    Ascend-Idle-Limit = "900"
testtwo          Password = "11111"
                    Service-Type = "Framed-User",
                    Session-Timeout = "9000",
                    Ascend-Idle-Limit = "900"
testthree        Password = "11111"
                    Framed-Address = "000.000.000.000",
                    Framed-Netmask = "255.255.255.0"
                    Ascend-Route-IP=Route-IP-Yes
                    Framed-Route = "000.000.000.000/29 000.000.000.000 1 n"
1testone        Password = "11111"
                    Service-Type = "Framed-User",
                    Ascend-Idle-Limit = "900"
testtwo5        Password = "11111"
                    Service-Type = "Framed-User",
                    Session-Timeout = "9000",
                    Ascend-Idle-Limit = "900"
So, could someone explain this? I understand that "/^[^ ]/ " grabs all the usernames. and I think I understand the ternary operator; found equals true (1) if name (the username) is found in $1, or found equals false (0) if it's not. Then I get a bit lost, I think !found toggles the value of found, but why? And how does it all end up removing the username and all text between it and the next username. Thanks, pete.
 
Old 10-14-2006, 06:39 PM   #2
coaic
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Registered: Apr 2006
Location: Australia
Distribution: Ubuntu, SuSE, FC, xBSD, Darwin/Fink
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awk code explanation

found remains set to 0 or 1 until the RE /^[^ ]/ matches again on a subsequent line in the data file. An expression in a script line that evaluates non zero results in the line being printed. You can check this by trying the following:

nawk '1' myFile.txt # all lines in the file are printed
nawk '0' myFile.txt # no lines in the file are printed

The RE in question only matches lines that have at least the first character in the line non blank.

Remember awk is a report scripting tool - all patterns in a script file are applied sequentially to each line as it is read from the data file with the exception of the BEGIN and END patterns which match before the first line of the data file and after the last line of the data file, respectively.

Last edited by coaic; 10-14-2006 at 06:41 PM.
 
Old 10-14-2006, 07:05 PM   #3
pete1234
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Thanks coaic, think I've got it now.
 
  


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