How to limit file size on commit?

This pre-commit hook will do the file size check:

.git/hooks/pre-commit

#!/bin/sh
hard_limit=$(git config hooks.filesizehardlimit)
soft_limit=$(git config hooks.filesizesoftlimit)
: ${hard_limit:=10000000}
: ${soft_limit:=500000}

list_new_or_modified_files()
{
    git diff --staged --name-status|sed -e '/^D/ d; /^D/! s/.\s\+//'
}

unmunge()
{
    local result="${1#\"}"
    result="${result%\"}"
    env echo -e "$result"
}

check_file_size()
{
    n=0
    while read -r munged_filename
    do
        f="$(unmunge "$munged_filename")"
        h=$(git ls-files -s "$f"|cut -d' ' -f 2)
        s=$(git cat-file -s "$h")
        if [ "$s" -gt $hard_limit ]
        then
            env echo -E 1>&2 "ERROR: hard size limit ($hard_limit) exceeded: $munged_filename ($s)"
            n=$((n+1))
        elif [ "$s" -gt $soft_limit ]
        then
            env echo -E 1>&2 "WARNING: soft size limit ($soft_limit) exceeded: $munged_filename ($s)"
        fi
    done

    [ $n -eq 0 ]
}

list_new_or_modified_files | check_file_size

Above script must be saved as .git/hooks/pre-commit with execution permissions enabled (chmod +x .git/hooks/pre-commit).

The default soft (warning) and hard (error) size limits are set to 500,000 and 10,000,000 bytes but can be overriden through the hooks.filesizesoftlimit and hooks.filesizehardlimit settings respectively:

$ git config hooks.filesizesoftlimit 100000
$ git config hooks.filesizehardlimit 4000000