Linux Environment Variables

 

Working with Environment Variables

To list all environment variables and their values use:

$ env

To display the value of some particular env var use echo $ENV_VAR_NAME. Example:

$ echo $GOPATH
/home/test_user/dev/go

To set environment variables for the single command:

Example:

$ env GOOS=linux GOARCH=amd64 go build cmd/main.go

From the executable's point of view, the same would have been achieved without using env:

$ GOOS=linux GOARCH=amd64 go build cmd/main.go

To set environment variables for the current terminal session:

$ export GOPATH=/mnt/c/dev/go

export is a bash builtin. export key=value is extended syntax and should not be used in portable scripts (i.e. #! /bin/sh)

What's the difference between set, export and env and when should I use each?
What is the difference between set, env, declare and export when setting a variable in a Linux shell?

If some bash script calls executable which requires some env variables, we also need to use export.Example:

demo.sh:

#!/bin/bash
...
echo
echo Env variables:
go env
export CGO_ENABLED=0
export GOOS=linux
export GOARCH=amd64 
echo
echo Env variables:
go env
go build -o './bin/myapp' -v './cmd/main.go'

...gives the output:

Env variables:
[16:33:25][Step 4/7] GOARCH="amd64"
[16:33:25][Step 4/7] GOOS="linux"
[16:33:25][Step 4/7] CGO_ENABLED="1"
...
[16:33:25][Step 4/7] 
[16:33:25][Step 4/7] Env variables:
[16:33:25][Step 4/7] GOARCH="amd64"
[16:33:25][Step 4/7] GOOS="linux"
[16:33:25][Step 4/7] CGO_ENABLED="0"
...

How do I add environment variables?
How to set an environment variable only for the duration of the script?

 

Linux Default Environment Variables

user@host:~/$ echo $HOSTNAME
host