bash-alias

#!/bin/sh
#
# Configure aliases in bash shell profile.
#
# By default considers the current user's profile, ~/.bashrc, a different file
# may be specified as argument.
#
# One or more alias definitions can be given as arguments with form
# "name=value", i.e. without the alias command itself first. The value part
# should be supplied unquoted, as the single quotes will be automatically added
# when creating the alias command: alias "name='value'". This will break if the
# value itself contains single quotes, so option --raw can be supplied if you
# want to take charge of the quoting yourself, then the entire string will be
# supplied to the alias command verbatim.
#
# The main advantages of using this script are simpler syntax for bulk creating
# multiple aliases, and checking for existing aliases. If an existing alias
# with same name exists that is reported, if the value is identical then the
# existing is kept, if not then the existing is commented out and the new one
# is added.
#
# Examples:
#   bash-alias "ls=ls --color=auto"
#   bash-alias --raw "ls='ls --color=auto'"
#   bash-alias ~/.bashrc "ls=ls --color=auto" "grep=grep --color=auto"
#   bash-alias --raw ~/.bashrc "ls='ls --color=auto'" "grep='grep --color=auto'"
#

if [ $# -lt 1 ]; then
    echo "Missing arguments" >&2
    echo "Usage: ${0} [--raw] [file] name=value..." >&2
    exit 1
fi

# Handle options.
# They may be anywhere in the list of arguments, looking for any prefixed
# with '-', except the special end of options marker "--", recognizing
# flag --raw, warning about any other.
raw=0
for arg in "$@"; do
    case "$arg" in
        --raw) raw=1 ;;
        --) break ;;
        -*) printf 'Unknown flag: %s\n' "$arg" >&2; exit 1 ;;
    esac
done
unset arg

# Handle file argument.
# Optional with fall-back to ~/.bashrc.
# This may be anywhere in the list of arguments, looking for the first that
# is not an option (handled above) and does not contain '=', assuming it must
# then be a file path.
file=""
for arg in "$@"; do
    case "$arg" in
        -*) continue ;; # Ignore (option, already handled)
        *=*) continue ;; # Ignore (alias, will be handled later)
        *)
            if [ -n "$file" ]; then
                printf 'Invalid argument (expected name=value): %s\n' "$arg" >&2
                exit 1
            fi
            file="$arg"
            ;;
    esac
done
unset arg
if [ -z "$file" ]; then
    file="${HOME}/.bashrc"
fi
if [ ! -f "$file" ]; then
    echo "Failed to find bash user profile '${file}'" >&2
    exit 1
fi

# Process aliases.
for definition in "$@"; do
    case "$definition" in
        *=*) ;;
        *) continue ;; # Ignore (already handled)
    esac
    name="${definition%%=*}" # %%=* strips from the first = to the end (the name)
    # Verify valid name.
    # Name is required, i.e. cannot be empty, definition cannot be just in form
    # "=value". Other than that name can be just about anything, however the
    # shell unconditionally interprets the first word before a space as the
    # command so in reality the name cannot contain space. This will also catch
    # arguments incorrectly including the alias command, e.g.
    # "alias ls='ls --color=auto'" (should be "ls=ls --color=auto").
    case "$name" in
        ''|*' '*) printf 'Skipping invalid alias (name is empty or contains space): %s\n' "$definition" >&2; continue ;;
    esac
    old=$(command -v "$name" 2>/dev/null)
    case "$old" in
        /*) printf "WARNING: Alias name '%s' will mask existing command (%s)\n" "$name" "$old" >&2 ;;
        ?*) printf "WARNING: Alias name '%s' will mask a shell builtin\n" "$name" >&2 ;;
    esac
    unset old
    name_escaped=$(printf '%s' "$name" | sed 's/[]\.^$*[]/\\&/g') # Escape BRE metacharacters
    value="${definition#*=}" # #*= strips up to and including the first = (the value)
    if [ "$raw" -eq 1 ]; then
        line="alias ${name}=${value}"
    else
        line="alias ${name}='${value}'"
    fi
    line_escaped=$(printf '%s' "$line" | sed 's/[]\.^$*[]/\\&/g')
    if grep -q "^${line_escaped}$" "$file"; then
        echo "Skipping ${line}: Already defined"
    else
        old=$(grep "^alias ${name_escaped}=" "$file")
        if [ -n "$old" ]; then
            echo "WARNING: Commenting out existing ${old}"
            sed -i "s/^\(\\s*alias\\s\+${name_escaped}=.*\)$/#\\1/" "$file"
        fi
        unset old
        echo "Adding ${line}"
        printf '%s\n' "${line}" >> "$file"
    fi
done
unset raw file definition name name_escaped value line line_escaped