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Top Forums UNIX for Dummies Questions & Answers Environment variable substitution in Linux make Post 302949253 by Corona688 on Wednesday 8th of July 2015 12:59:44 PM
Old 07-08-2015
You can use the ?= operator, which sets a variable if and only if it's not already set:

Code:
VAR ?= value

 

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GIT-VAR(1)							    Git Manual								GIT-VAR(1)

NAME
git-var - Show a Git logical variable SYNOPSIS
git var ( -l | <variable> ) DESCRIPTION
Prints a Git logical variable. OPTIONS
-l Cause the logical variables to be listed. In addition, all the variables of the Git configuration file .git/config are listed as well. (However, the configuration variables listing functionality is deprecated in favor of git config -l.) EXAMPLE
$ git var GIT_AUTHOR_IDENT Eric W. Biederman <ebiederm@lnxi.com> 1121223278 -0600 VARIABLES
GIT_AUTHOR_IDENT The author of a piece of code. GIT_COMMITTER_IDENT The person who put a piece of code into Git. GIT_EDITOR Text editor for use by Git commands. The value is meant to be interpreted by the shell when it is used. Examples: ~/bin/vi, $SOME_ENVIRONMENT_VARIABLE, "C:Program FilesVimgvim.exe" --nofork. The order of preference is the $GIT_EDITOR environment variable, then core.editor configuration, then $VISUAL, then $EDITOR, and then the default chosen at compile time, which is usually vi. GIT_PAGER Text viewer for use by Git commands (e.g., less). The value is meant to be interpreted by the shell. The order of preference is the $GIT_PAGER environment variable, then core.pager configuration, then $PAGER, and then the default chosen at compile time (usually less). SEE ALSO
git-commit-tree(1) git-tag(1) git-config(1) GIT
Part of the git(1) suite Git 2.17.1 10/05/2018 GIT-VAR(1)
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