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Shell Programming and Scripting
Meaning of NF{ a[$1]=a[$1]" "$2 ; next }?
Post 302389754 by Scott on Monday 25th of January 2010 06:25:06 PM
01-25-2010
Hi.
It's part of an awk script.
NF{...} means if there are more than zero fields in the current record (i.e. not a blank line) perform the action between { and }
An awk script is made up of patterns (conditions, really) and actions
PATTERN { ACTION }
If PATTERN evaluates to true, then ACTION is performed.
[NF is an awk variable giving the number of fields in the current record. If it's non-zero, ACTION is performed.]
{ a[$1]=a[$1]" " $2; next } means append the value of field two ($2) to an array (a) indexed by the value of field one ($1).
The END section is performed after all input files are processed.
for(i in a) means assign to i, in turn, each element of a
and print the index value i, followed by the value referenced by that index (a[i]).
The two lines you posted say: add field two to an array called a, indexed by distinct values of field one.
HTH
It's part of an awk script.
NF{...} means if there are more than zero fields in the current record (i.e. not a blank line) perform the action between { and }
An awk script is made up of patterns (conditions, really) and actions
PATTERN { ACTION }
If PATTERN evaluates to true, then ACTION is performed.
[NF is an awk variable giving the number of fields in the current record. If it's non-zero, ACTION is performed.]
{ a[$1]=a[$1]" " $2; next } means append the value of field two ($2) to an array (a) indexed by the value of field one ($1).
The END section is performed after all input files are processed.
for(i in a) means assign to i, in turn, each element of a
and print the index value i, followed by the value referenced by that index (a[i]).
The two lines you posted say: add field two to an array called a, indexed by distinct values of field one.
HTH
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ppm(5) AUTHOR
Copyright (C) 1991 by Rick Vinci. 26 April 1991 ppmtosixel(1)