awk note

[gkernel]

awk '/pattern/ {program}'

[gkernel]

awk 'BEGIN {<initializations>}
<search pattern 1> {<program actions>}
<search pattern 2> {<program actions>}
...
END {<final actions>}'

print $1 $2 // concatenate
print $1,$2 // seperate by space

NR: number of records
NF: number of fields

any string is a variable

awk -f program_file_name

printf("<format>", <parameters>); # same as C

comments: #

[gkernel]

awk -F <delimiter>
awk <vars> # e.g. awk a=1 x=123

search pattern:
$1 !~ /abc/ # ~ is ==
$1 != "abc"
/start/,/end/
NR==1,NR==10
NF=0
(NR >= 30) && ($1 == "china") # && and ||
(($1+0) == $1) # ture if $1 is a number (a trick)

number (only in base 10):
123
3.14
-2.1e10

[gkernel]

修正错误：~不是==，~和//连用，==和""连用

[Sunyata]

NR: number of records
NF: number of fields
FILENAME: current input file name
FS: field separator
RS: record separator
OFS: output field separator
ORS: output record separator
OFMT: format for numeric output

change input: $n="" # n is a number
array: arr[1], arr["one"]

exponentiation: ^

functions:
length, length(<string>)
substr(<string>, <start>, <len>)
split(<string>, <array>, [<separator>])
index(<string>, <searchstring>) # 1 based

for (<var> in <array>) {
}

next: get another line of input

print, printf, sprintf # can use redirection operator: print $1 > file