What does the export command do

Question

I am a little new to Linux  and I happen to run some commands blindly  in order to get things done  I thought that it will not be a waste of asking these type of questions  since more new people would have a regular knowledge about those   I started to work with Jenkins recently  and then I had to use this export command to run the Jenkins war archive  So I needed to know what export command does in general  and why we need to run this command  while running Jenkins  after the Jenkins home is set    Thanks

User · Accepted Answer

export in sh and related shells  such as bash   marks an environment variable to be exported to child-processes  so that the child inherits them   export is defined in POSIX      The shell shall give the export attribute to the variables corresponding to the specified names  which shall cause them to be in the environment of subsequently executed commands  If the name of a variable is followed by   word  then the value of that variable shall be set to word

User · Answer

In simple terms  environment variables are set when you open a new shell session  At any time if you change any of the variable values  the shell has no way of picking that change  that means the changes you made become effective in new shell sessions  The export command  on the other hand  provides the ability to update the current shell session about the change you made to the exported variable  You don t have to wait until new shell session to use the value of the variable you changed

User · Answer

I guess you re coming from a windows background  So i ll contrast them  i m kind of new to linux too    I found user s reply to my comment  to be useful in figuring things out   In Windows  a variable can be permanent or not  The term Environment variable includes a variable set in the cmd shell with the SET command  as well as when the variable is set within the windows GUI  thus set in the registry  and becoming viewable in new cmd windows  e g  documentation for the set  command in windows  https   technet microsoft com en-us library bb490998 aspx   Displays  sets  or removes environment variables  Used without parameters  set displays the current environment settings      In Linux  set does not display environment variables  it displays shell variables which it doesn t call refer to as environment variables  Also  Linux doesn t use set to set variables apart from positional parameters and shell options  which I explain as a note at the end   only to display them and even then only to display shell variables  Windows uses set for setting and displaying e g  set a 5  linux doesn t     In Linux  I guess you could make a script that sets variables on bootup  e g   etc profile or  etc  bashrc but otherwise  they re not permanent   They re stored in RAM     There is a distinction in Linux between shell variables  and environment variables   In Linux  shell variables are only in the current shell  and Environment variables  are in that shell and all child shells    You can view shell variables with the set command   though note that unlike windows  variables are not set in linux with the set command    set -o posix  set   doing that set -o posix once first  helps not display too much unnecessary stuff   So set displays shell variables   You can view environment variables with the env command  shell variables are set with e g  just a   5  environment variables are set with export  export also sets the shell variable  Here you see shell variable zzz set with zzz   5  and see it shows when running set but doesn t show as an environment variable   Here we see yyy set with export  so it s an environment variable  And see it shows under both shell variables and environment variables    zzz 5    set   grep zzz zzz 5    env   grep zzz    export yyy 5    set   grep yyy yyy 5    env   grep yyy yyy 5      other useful threads  https   unix stackexchange com questions 176001 how-can-i-list-all-shell-variables   https   askubuntu com questions 26318 environment-variable-vs-shell-variable-whats-the-difference  Note- one point which elaborates a bit and is somewhat corrective to what i ve written  is that  in linux bash    set  can be used to set  positional parameters  and  shell options attributes   and technically both of those are variables  though the man pages might not describe them as such  But still  as mentioned  set won t set shell variables or environment variables    If you do  set asdf then it sets  1 to asdf  and if you do echo  1 you see asdf    If you do set a 5 it won t set the variable a  equal to 5  It will set the positional parameter  1 equal to the string of  a 5    So if you ever saw set a 5 in linux it s probably a mistake unless somebody actually wanted that string a 5  in  1  The other thing that linux s set can set  is shell options attributes  If you do set -o you see a list of them  And you can do for example set -o verbose  off  to turn verbose on btw the default happens to be off but that makes no difference to this   Or you can do set  o verbose to turn verbose off   Windows has no such usage for its set command

[shell] What does the 'export' command do?

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