variables

$BASH_VERSION

$RANDOM

$SECONDS

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cat pid.sh

echo "Process $$ Starting up with arguments $@ for parent $PPID"

$$ special variable which provides the process ID of this shell itself

PPID is set to the process ID of the process that called this shell or shell script

./pid.sh 1

Process 26249 Starting up with arguments 1 for parent 19260

SECONDS – returns a count of the number of seconds the shell has been running

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echo $HOME

/home/ok74010

PATH is a colon-separated list of directories used to find program files. It’s searches left-to-right

You can read a list of hashed paths by running hash –l, to remove hash –r

In PATH, a period (.) is used to represent the current directory of the calling program.

Less well known is that a double colon (: :) will do the same, and a single colon at the beginning or end of the PATH variable will also expand to the current working directory.

From security perspective, it is very bad practice to put a dot . in your PATH, especially at the front of the PATH.

echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games

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$ ll fil??

$ ls f*a*

$ ls a?b*

$ ls –ld /etc/rc{0,1,2,3,4}.d

ll fi{l,w}?

-rw-r--r-- 1 0 Jul 20 14:36 fil2

-rw-r--r-- 1 0 Jul 20 08:35 file

-rw-r--r-- 1 0 Jul 20 14:36 fiw2

fi[a-z]?

-rw-r--r-- 1 0 Jul 20 14:36 fil2

-rw-r--r-- 1 0 Jul 20 08:35 file

-rw-r--r-- 1 0 Jul 20 14:36 fiw2

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[shell scripting p40]

ubuntu2@ubuntu2:~/temp$ cat var1

#!/bin/bash

echo “My name is `basename $0` - I was called as $0”

echo “I was called with $# parameters.”

count=1

while [ "$#" -ge "1" ]; do

echo “Parameter number $count is: $1”

let count=$count+1

shift

done

ubuntu2@ubuntu2:~/temp$ 

ubuntu2@ubuntu2:~/temp$ bash var1 1 2 3

“My name is var1 - I was called as var1”

“I was called with 3 parameters.”

“Parameter number 1 is: 1”

“Parameter number 2 is: 2”

“Parameter number 3 is: 3”