A simple program to parse git describe

gitdesc.sh command [-r]

Where command is one of:

• all - entire git describe in --long format with or without tags
• commit - commit, omitting leading v (if applicable)
• tagrev - tag revision count
• major - major release version
• ninor - minor release version
• micro - micro release version
• version - M.m.c

and option is

• -r -- get release tag only

gitdesc.sh is a small utility to return elements from git describe and echo them to terminal. It can be used to assign variables in a configure.ac file using m4 defines. It can be used by package managers to enhance package versioning. Using simple bash commands, gitdesc.sh can be easily modified and adapted through creative use of cut and ${string/manipulation/commands}

It eleminates the need to hard code versions into configure.ac or other files. Rather, it relies on git itself to provide versioning information - either from tags or release (annotated) tags.

If there is no .git directory, then a VERSION file can be used with the following lines. This may occur if your project is downloaded as a tarball. In this case, no .git directory will exist.

# Version file
# in case tarball downloaded

Major: 0
Minor: 0
Micro: 0

Or Adjust as necessary

Place gitdesc.sh in your path or call directly. If using in a git repository, place where needed.

Assigning m4 variables can be tricky. calling gitdesc.sh for the m4_esyscmd_s command can make it easier.

First task is to strip the git describe command of any extra values. All activity is contained in the init() function.

# git describe raw format
describe_tag=$(git describe $tagopt --long --abbrev=$commit_length)
# if tag has a leading `v' this will remove
describe_tag=${describe_tag/v/}
describe_tag=${describe_tag/g/}

The result will be
some.version-R-1234567

where `R' is a revision count from last tag, 0 - n.

From there, further string manipulations can occur. Here is the major version getting stipped out.

version=$(echo $describe_tag | cut -d- -f1)
# assign major version
major=$(echo $version | cut -d. -f1)

If a VERSION file is used, then it will assign Major, Minor, and Micro as needed.

And so on. Configure to taste. It's possible different repos will have different formats and requirements.

In these examples, gitdesc.sh is in the util directory of the git repo.

m4_define([v_maj], [m4_esyscmd_s([./util/gitdesc.sh major])]) This line will assign the major version from the latest tag to the m4 variable v_maj.

m4_define([v_full], [m4_esyscmd_s([./util/gitdesc.sh all])]) This line will assign the entire git describe output to the variable v_full.

m4_define([v_maj], [m4_esyscmd_s([./util/gitdesc.sh major])])  
m4_define([v_min], [m4_esyscmd_s([./util/gitdesc.sh minor])])  
m4_define([v_mic], [m4_esyscmd_s([./util/gitdesc.sh micro])])  
m4_define([v_ver], [v_maj.v_min.v_mic])  

The Advanced Bash Scripting Guide, and in particular table B-5 (linked here) has every trick you may need to tailor gitdesc.sh to your needs.

Inspiration for this program came from Thomas Adam,of the fvwm3 window manager which used a similarly applied script.

Free to use for commercial or non-commercial use. Attribution is appreciated.

Peter Hyman
December 2020, April 2021
[email protected]