Linux environment variables

Which LS (you can see the exact location of LS, LS is a file)

LS ==> ls--color=auto

alias (alias)

which command: Used to find the absolute path to a command .

[[email protected] ~]# which LS

Alias ls= ' ls--color=auto '

/bin/ls

lsis aSpecial command., usingaliasCommandmade an alias.. We used it.lsis actually/bin/ls--color=auto', plus--color=auto, it's colored, otherwise it's all black and white..

alias can be to set the alias of a command can also setting aliases for files .

alias usage of , usually in the work we often use some of the command is longer, each shot to need a good time, then you can use alias to make a short alias, speed up.

Example: (change the NIC configuration File command Vi/etc/sysconfig/network-scripts/ifcfg-eth0)

[[email protected] ~]# alias vieth= ' Vi/etc/sysconfig/network-scripts/ifcfg-eth0 '

[Email protected] ~]# Vieth

The configuration file of the NIC appears after running

Device=eth0

Hwaddr=00:0c:29:bf:07:da

Type=ethernet

uuid=454cbf99-9d6c-40a7-a8f7-646870324602

Onboot=yes

Nm_controlled=yes

Bootproto=static

ipaddr=192.168.1.103

netmask=255.255.255.0

gateway=192.168.1.1

dne1=192.168.1.1

dns2=8.8.8.8

~

~

~

Type:quit<enter> to Exit Vim

This will directly edit the configuration file, and then use which to see.

[email protected] ~]# which Vieth

Alias Vieth= ' Vi/etc/sysconfig/network-scripts/ifcfg-eth0 '

/bin/vi

In this way, the next time you edit the network card configuration file, you can directly use the Vieth command to operate, simple and convenient. To cancel this alias , you only need to unalias vieth .

which This command is usually used only to Query the absolute path of a command , not used frequently.

alias (alias), /bin/ls (absolute path of LS)

Why do we enter a lot of commands without having to use the absolute path of the commands?

This is because the environment variable path is in effect.

Please enter Echo $PATH , here's Echo is actually Print the meaning of, while PATH the front $ indicates that a variable is followed by a .

[Email protected] ~]# echo $PATH

/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

Because/bin is in the path setting, it is natural to find LS. If the LS is moved under the/root, and then itself is under the/root, but when the execution of LS, he just ignore you, how to do?

This is because the bad environment variable path does not/root this directory, and the LS moved to the bottom of/root, the natural system can not find the executable file, so you will be prompted: Command not found ! (the command was not found)

[Email protected] ~]# mv/bin/ls/root/

[[email protected] ~]# ls

-bash:/bin/ls: No file or directory

MV used to move a file or directory , you can also Renaming .

So how to overcome this problem?

There are two methods, one of which is Add the/root path directly to the $path !

How to increase?

Command can be used to add commands path= $PATH:/root:

[Email protected] ~]# path= $PATH:/root

[Email protected] ~]# echo $PATH

/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin: /root

[[email protected] ~]# ls

Anaconda-ks.cfg install.log Install.log.syslog ls

The other approach is to use Absolute Path :

[Email protected] ~]#/root/ls

Anaconda-ks.cfg install.log Install.log.syslog ls

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Linux environment variables