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For example in this awk tutorial there are three examples:
tolower($1) ~ /mary/ { print "CI Record: " $0; }$0 !~ /Mary/ { print "Not Mary: " $0; }$1 == "Mary" { print "Mary Record: " $0; }
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You use a dollar sign (' $ ') to refer to a field in an awk program, followed by the number of the field you want. Thus, $1 refers to the first field, $2 to the second, and so on. (Unlike in the Unix shells, the field numbers are not limited to single digits.
The variable $1 represents the contents of field 1 which in Figure 2 would be "-rwxr-xr-x." $2 represents field 2 which is "1" in Figure 2 and so on. The awk variables $1 or $2 through $nn represent the fields of each record and should not be confused with shell variables that use the same style of names.
awk '{ print $2; }' prints the second field of each line. This field happens to be the process ID from the ps aux output. xargs kill -${2:-'TERM'} takes the process IDs from the selected sidekiq processes and feeds them as arguments to a kill command.
'{print $4}' means print the fourth field (the fields being separated by : ).
In awk, $0 is the whole line of arguments, whereas $1 is just the first argument in a list of arguments separated by spaces. So if I put "Mary had a little lamb" through awk, $1 is "Mary", but $0 is "Mary had a little lamb". The second line is trying to find the substring "Mary" in the whole line given to awk.
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