stefaanc/globals

use global variables in a bash shell

Global Variables for Bash

a small library to provide a form of global variables in a bash shell

The library can be taken from the scripts folder, put in your folder with scripts, and dot-source in your scripts.

. ./.globals.bash

The functions provided:

• global is used to set a global variable. It is used like one uses the export statement or the local statement in a function.

  global MY_VAR="some value"

  • The variable is set in the current environment.
  • The variable is exported in the current environment, so it is available in the environments of all future child-shells.
  • The variable is set in the environments of the chain of parent-shells that used call to eventually run this script.
  • The variable is exported in the environments of these parent-shells, so it is available in the environments of all future child-shells of these parent-shells.

• call is used to execute a script, pickup all global variables set by that script and its call-ed child-scripts, and inject these global variables in the current environment.

  call ./my-script

  • call uses bash to execute the script
  • The exitcode of the executed script is returned in $?
  • A global variable $LASTEXITCODE is set to the $? value of the last call-ed script
  • A global variable $GLOBALS_INJECT is reserved to communicate the dynamically created filedescriptor of the inject-stream between calling and called scripts. This inject-stream is used to send the required information to set global variables, from the called script back to the calling script. This inject-stream is only open for as long as the called script is running.

Example

Let's make three scripts

• test-globals-1.bash calls test-globals-2.bash

  . ./.globals.bash
  
  echo "### test-globals-1.bash"
  echo ""
  
  call ./test-globals-2.bash
  
  echo "\$?=$?"
  echo ""
  
  echo "### test-globals-1.bash"
  echo "\$LASTEXITCODE=$LASTEXITCODE"
  echo "\$MY_VAR=$MY_VAR"
  echo "###"
  echo ""

• test-globals-2.bash calls test-globals-3.bash

  . ./.globals.bash
  
  echo "### test-globals-2.bash"
  echo ""
  
  call ./test-globals-3.bash
  
  echo "\$?=$?"
  echo ""
  
  echo "### test-globals-2.bash"
  echo "\$LASTEXITCODE=$LASTEXITCODE"
  echo "\$MY_VAR=$MY_VAR"
  echo "###"
  echo ""
  
  exit $LASTEXITCODE

• test-globals-3.bash set a global variable

  . ./.globals.bash
  
  echo "### test-globals-3.bash"
  echo ""
  
  global MY_VAR="some value"
  
  echo "### test-globals-3.bash"
  echo "\$LASTEXITCODE=$LASTEXITCODE"
  echo "\$MY_VAR=$MY_VAR"
  echo "###"
  echo ""
  
  exit 42

Now run

./test-globals-1.bash

The result is:

### test-globals-1.bash

### test-globals-2.bash

### test-globals-3.bash

### test-globals-3.bash
$LASTEXITCODE=
$MY_VAR=some value
###

$?=42

### test-globals-2.bash
$LASTEXITCODE=42
$MY_VAR=some value
###

$?=42

### test-globals-1.bash
$LASTEXITCODE=42
$MY_VAR=some value
###

ℹ️
The scripts folder contains a more elaborate version of the above scripts.

For Further Investigation

• use the same techniques to return results to the caller of a script