Question

I’ve watched an excellent shell scripting course through a multitude of videos. Now that I think I am fairly familiar with the Bourne shell, I decided to write my first shell script.

Script goal: check if git working directory is clean. If so, overwrite working directory to a branch named deployment. Finally, push the deployment branch to origin.

I ended up with this code:

#!/bin/sh

######################################################
# Deploys working directory to git deployment branch.
# Requires that the working directory is clean.
######################################################

#check if the working directory is clean
if [ git diff-index --quiet HEAD ]
then
    if [ git branch -f deployment ]
    then
        if [ git push origin deployment ]
        then
            echo
            echo "OK. Successfully deployed to git deployment branch."
            echo
            exit 0 #success
        else
            echo
            echo "Error: failed to push deployment branch to origin."
            echo
            exit 1 #failure
        fi
    else
        echo
        echo "Error: failed to create or overwrite deployment branch."
        echo
        exit 1 #failure
    fi
else
    echo
    git status #show the status of the working directory
    echo
    echo "Error: working directory is not clean. Commit your changes first..."
    echo
    exit 1 #failure
fi

Unfortunately, this seems to give me an error: ./tools/deploygit: 9: [: git: unexpected operator

Why is this so? What operator am I using in if [ git diff-index --quiet HEAD ] that is unexpected?

As a bonus, do you have any suggestions or tips on how to improve the efficiency, logic or readability of this script?

Answer 1

In this statement:

if [ git diff-index --quiet HEAD ]

The [ is an alias for the test command, so what you’re actually running is…

if test git diff-index --quiet HEAD ]

…which isn’t what you mean. You don’t need to use the test command in order to evaluate the result of a command; you should just do this:

if git diff-index --quiet HEAD

Take a look at the documentation for the if command:

$ help if
if: if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ]... [ else COMMANDS; ] fi

The conditional argument to the if statement is command. Normally, the test command is used to make it look like other languages, but you can put any command there. Things that exit with a return code of 0 evaluate to true and anything else evaluates to false.