A, awk works
Two, awk usage
awk [the Option] ... 'Program' FILE ...
1, Program statement must use single quotes!
2, a plurality of program statements used together with curly braces, can be parallel, can be nested
three, awk common parameters
-F # specify the delimiter
Example: awk -F: The first column is the delimiter: '{print $ 1}' / etc / passwd # output / etc / passwd / file in
-v # because awk is a language compiler, you can define their own variables, but also has its own built-in variables (variables and the shell ring similar), so to manually specify variable parameters.
Example: awk -va = "a + b" '{print a}' test.txt # to a copy, print a variable (variable does not need to call in awk added $ symbol)
Four, awk's syntax
1.print # default output
In the awk command is not saved, we can associate other awk command to save the results of
示例：awk '{a="a+b";print a}' test.txt | tee a.txt
2.printf # achieve formatted output
Example: printf "% s% d is the best class for" variable 1, variable 2
(1) character format
String% s
% d% i value
% e% E scientific calculation value
% c ACSii code value
% f float
% u unsigned integer
%%% escape character only display their
(2) Modifiers
The default is right-aligned
- on behalf of Left
Median% 5.4f # 5 representatives share, taken on behalf of 4 decimal places
3. Variables
Variables into built-in variables and custom variables
Built-in variables are variables awk language supported by default
variable:
FS # delimiter defining input variables
OFS # define the output variable delimiter
NF # line separator after the number of parameters defined (the last one variable partition after $ NF)
Example: awk -v FS = ":" '/ \ / bash $ / {print $ 1, $ NF}' / etc / passwd
File number of rows NR definition file, define multiple files, line numbers superimposed
FNR file count only their own line number
Example: awk '{print NR}' / etc / fstab / etc / passwd
awk '{print FNR}' /etc/fstab /etc/passwd
FILENAME name of the file is stored
Example: awk '{print FILENAME}' / etc / passwd # N times to print the file name, the file number of rows N
BEGIN {} while statement cycle start line only performed once;
Example: awk 'BEGIN {print FILENAME}' / etc / passwd