Working with the Unix OS

Unix Tools
Let an example input file "countries", contain fields "country", "area", "population", "continent"
awk '{ print $2, $1 }' filel # output column 2 & 1
awk '{ print NR, $0 }' filel # add line numbers
awk '{ printf "%10s %6d %6d\n", $1, $2 ,$3 }' filel
{ if ($4 == "ASIA") print > "ASIA"
if ($4 == "EUROPE") print > "EUROPE"}
{ if ($2 == "XX") print | "mail joe" }
{ print $1 | "sort" }
{ print ... | "cat -v > /dev/tty" }
! Patterns
Certain words
BEGIN { FS="\t"
printf "Country\t\tArea\tPopulation\tContinent\n\n"
}
{ printf "%-10s\t%6d\t%6d\t\t%-14s\n", $1,$2,$3,$4 }
END { print "The number of records is", NR }
Arithmetic relational expressions
$3 >100
Regular expressions
/xly/ # contains either x or y
/ax+b/ # 1 or more x's between a and b
/ax?b/ # 0 or more x's between a and b
/a.b/ # any character between a and b
/ax*b/ # 0 or more x’s between a and b
Combinations of above
$2 >= 3000 && $3 >= 100 # AND
$4 == "Asia" || $4 == "Africa" # OR
$4 ~ /"Asia|^"Africa/ # matches
! Pattern Ranges
patternl, pattern2 ( action )
# all lines between pattern1 and pattern 2
e.g.
/Canada/,/Brazil/ {…}
NR == 2, NR == 5 {…}
! Actions
Sequence of action statements separated by newlines
# expressions
{ print $1, (1000000 * $3) / ($2 * 1000)}
# variables
/Asia/ { pop += $3; ++n }
END { print "total population of", n, "Asian countries is", pop }
# initialisation of variables
maxpop < $3 {
maxpop = $3
country = $1
}
END { print country, maxpop }
# field variables
48