A script need help


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# 8  
Quote:
Originally Posted by Chubler_XL
Glad to explain what is going on in this code. Working thru and understanding is a great way to improve your awk skills.

Field separator RE [=\\][]

This is a simple bracket [] expression and matches any of the following characters as a field separator =, ] and [.
the ] character needs to be escaped in the RE to stop it being interpreted as a close bracket for the list.
We also need to escape the escape to stop the shell eating it up before it's passed to awk.

After the init section the two arrays are populated as follows:
Code:
keypos[1]=RECORD_COUNT
keypos[2]=VALUE2
keypos[3]=VALUE3

keys[RECORD_COUNT]="MISSING"
keys[VALUE2]="MISSING"
keys[VALUE3]="MISSING"

The main use of keypos is to ensure the output is ordered the same as the want list.
If we just iterated thru keys[] the order is arbitrary and may change for different implementations of awk.
In prnsection() we use a for loop starting at i=1 and finishing when i is no longer in keypos ([icode]i in keypos[/code])

They key array is initialized to "MISSING" at the start and at each new section header.

$1 in keys { keys[$1]=$0 };
This code updates the key array when $1 (the part in front of the = sign) is in keys[].

The argument in awk server two purposes 1 is for input purposes the 2nd is to define local variables.
Actual arguments should be specified first followed by any local variables.
Here there are not arguments and i is simply a local variable to prnsection().
Its a good habit to always use local variables in functions unless there is a reason for them to be
global. Imagine if you had a for loop using a counter i and i was not local in prnsection(),
the i would be changed by the function call.

thanks for your explanation. I first though -F'[=\\][]' is multi delimiter too, but after run below command I lost.
Code:
:/apps >echo "[abcde]"|awk -F'[=\\][]' '{print NF}'
2
:/apps >echo "abc=123"|awk -F'[=\\][]' '{print NF}'
1
:/apps >uname -a
SunOS  5.10 Generic_150400-64 sun4v sparc sun4v

Image
# 9  
On Sun OS you need to use nawk or /usr/xpg4/bin/awk as the legacy Solaris awk is missing many POSIX features.
This User Gave Thanks to Chubler_XL For This Post:
# 10  
Some awk versions have a problem with parsing a complicated FS.
The following variant takes a simple FS:
Code:
awk -v want="CITY,REGION,STREET" '
function prnsection() {
   if (length(section)) {
     printf "%s",section
# quick loop in random order:
#    for (i in keypos)
# keep the order:
     for (i=1;i in keypos;i++) {
       printf " %s", keys[keypos[i]]
       keys[keypos[i]]="MISSING"
     }
     printf "\n"
   }
}
BEGIN {
   FS="="
# split puts CITY,REGION,STREET to keypos[1,2,3]
# the loop creates keys[CITY,REGION,STREET]
   for (i=split(want, keypos, ",");i;i--) {
       keys[keypos[i]]="MISSING";
   }
}
/^\[/ { prnsection(); section=$0 }
($1 in keys) { keys[$1]=$0 }
END { prnsection() }' infile

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