C2110 UNIX and programming Lesson 12 -1C2110
UNIX and programming
Petr Kulhanek
kulhanek@chemi.muni.cz
National Center for Biomolecular Research, Faculty of Science
Masaryk University, Kamenice 5, CZ-62500 Brno
Lesson 12
PS / 2020 Distance form of teaching: Rev2
C2110 UNIX and programming Lesson 12 -2Summary
L10
➢ AWK
C2110 UNIX and programming Lesson 12 -3The
process of executing the script
open
file?
Yes
No
parse record
(split into words)
execute the block
initialization
S
BEGIN {
}
{
}
/PATTERN/ {
}
END {
}
1
2
3
4
finalization
load
record
(row)?
No
Yes
execute the block
record
matches
PATTER?
Yes
No
E
user scriptlogic of AWK interpreter
variables are global (unless specified otherwise)
script.awk
C2110 UNIX and programming Lesson 12 -4Starting
AWK scripts
Text file processing:
$ awk –f script.awk input1.txt input2.txt
$ awk –f script.awk < vstup.txt
$ cat soubor.txt | awk –f script.awk
awk script
analyzed text files
result is printed on the screen
Analyzed data can be sent via standard input:
language interpreter
Indirect start:
C2110 UNIX and programming Lesson 12 -5-
Variables
Special variables:
NF number of fields in the current record (Number of Fields)
NR order of processed record (Number of Records)
$0 whole record
$1, $2, $3 ... individual record fields
Variable value:
print A + C;
print B;
Assignment to a variable:
A = 10;
B = "this is a text "
C = 10.4567;
D = A + C;
character $ allows programmatic access to individual fields of the record
Example:
for(i=1; i < NF; i++){
sum += $i;
}
C2110 UNIX and programming Lesson 12 -6Next
Subject
➢ AWK
C2110 UNIX and programming Lesson 12 -7-
Obsah
➢ AWK
• Conditions, logical operations
• Run control (next, exit)
• Loops
• Arrays