CMD List [11]

Arithmetic Function (awk)

Option or argument	Function
atan2(y,x)	For nawk. Return the arctangent of y/x in radians.
cos(x)	Return the cosine of x
exp(arg)	Return the natural exponent of arg
int(arg)	Return the integer value of arg
log(arg)	Return the natural logarithm of arg
rand()	For nawk. Generate a random number between 0 and 1.
sin(x)	Return the sine of x
sqrt(arg)	Return square root of arg
srand(expr)	For nawk. Use expr to set a new seed for random number generator. Default is time of day.

 

e.g.

awk '{if($3~/48/) print $0}' grade.txt

who | awk '{print $1 " " $NF " is good."}'

 

Calculation & END

ls -l | awk '{ totalsize += $5; print totalsize }'

512

1024

2048

ls -l | awk '{ totalsize += $5; print totalsize }' | tail -1

ls -l | awk '{ totalsize += $5 } END { print totalsize }'

 

Script & Array & Looping – for

awkscript

{

count[length($1)]++

}

END {

for (i=1; i < 9; i++)

print “There are “ count[i] “ accounts with “ i “ letter names.”

}

awk -F: -f awkscript < /etc/passwd

 

Condition – if

awk -F: ‘{ if (length($1) == 1) print $0 }’ < /etc/passwd

ls -l | awk '{if($1=="-rw-r-----") print $9}'

 

1          Error Message

M – message; S – solution.

M: &FILE=/sysp/cdclient/ndm/cfg/cliapi/ndmapi.cfg:&OSERR=13:&OSMSG=Permission denied

S: remove existing log.

 

2          Administration

 

2.1         Get Disk Space

Trimming a Directory - creating new files can make a directory bigger, deleting new files doesn't, it can never get smaller, unless you delete it.

e.g. 1. mv project project.toobig 2. mkdir project 3. mv project.toobig/*.txt project 4. rm -r project.toobig

 

Huge Files Might Not Take a Lot of Disk Space (if a lot of NUL characters in it), ls -ls to find the space allocation.

 

2.2         DOS ftp AIX

ftp <ip>

rename <original name> <new name>

put <local file> <remote file>

asc,pwd,dir,ls,rm,del,bye,Ctrl + C

 

3          Perl

Summary

1) Full name is “Practical Extraction and Report Language”. Slogan “There's More Than One Way To Do It”.

2) Automatically initialize variables and arrays start with a null or 0 value.

3) Like C, PERL statements must end in a semicolon (;).

4) Comments begin with a pound sign (#).

5) First line should mark with #!/usr/local/bin/perl. E.g.

#!/usr/bin/perl -w    # prompt warning

6) list use (), string use ‘’ or “”.

7) compare with Double quotes (“”), Apostrophe (‘’): 1 – can’t replace variable 2 – 反斜线不支持转义字符. 3 – 可以跨多行.

'' – Single Quote / Apostrophe, string no variable replacement

"" - Double quotes, string with variable replacement

`` - Backquote / Backtick, run the command, generate output as input

8) Automatically transform string into numeric. E.g. $result = "12a34" +1; # $result = 13

 

Argument

-e	used to enter one line of program. If -e is given, Perl will not look for a filename in the argument list.
-p	A –p overrides a –n switch. It causes Perl to assume the following loop. while (<>) {        ...           # your program goes here     } continue {        print or die "-p destination: $!\n";     }

 

Data Type

Scalars	纯量, string, number, or a reference. Denoted by $
Arrays of scalars	ordered lists of scalars indexed by number, starting with 0. Denoted by @. Arrays of scalars are faster than associative arrays.
Hashes	known as ‘associative arrays (of scalars)’, unordered collections of scalar indexed by string. Denoted by %

Note: Not divide data type into string, integer and float.