Manages Claude/Codex credential files to make it quick and easy to switch between accounts when a session limit is hit (only works on Linux since Mac uses keychain)

cas

#!/usr/bin/env bash
# cas - Claude/Codex Account Switch
# Switches a tool's live auth file to an aliased credentials file.
#
# Claude aliases: ~/.claude/.credentials.<alias>.json
# Codex aliases:  ~/.codex/auth.<alias>.json
#
# The selected alias carries a ".cur" tag. If a tool replaces the symlink
# during token refresh, cas uses that marker to recover the refreshed file.

set -euo pipefail

TOOLS=(claude codex)
TOOL=""
TOOL_DIR=""
LINK_NAME=""
FILE_PREFIX=""

usage() {
    cat >&2 <<'EOF'
Usage:
  cas <tool> <alias>  Switch <tool> to <alias>
  cas <tool>          Show the current account for <tool>
  cas                 Show current accounts
  cas -h, --help      Show this help

Tool names support unique partial matches:
  cas cl work         # Claude
  cas co 2            # Codex

When only ~/.claude or ~/.codex exists, a single argument is treated as the
alias for that tool:
  cas work
EOF
}

configure_tool() {
    TOOL="$1"
    case "$TOOL" in
        claude)
            TOOL_DIR="$HOME/.claude"
            LINK_NAME=".credentials.json"
            FILE_PREFIX=".credentials."
            ;;
        codex)
            TOOL_DIR="$HOME/.codex"
            LINK_NAME="auth.json"
            FILE_PREFIX="auth."
            ;;
        *)
            echo "Error: unsupported tool '$TOOL'." >&2
            exit 1
            ;;
    esac
}

match_tool() {
    local requested="$1" tool match=""
    for tool in "${TOOLS[@]}"; do
        if [[ "$tool" == "$requested"* ]]; then
            if [ -n "$match" ]; then
                echo "Error: tool '$requested' is ambiguous ($match, $tool)." >&2
                return 1
            fi
            match="$tool"
        fi
    done
    if [ -z "$match" ]; then
        echo "Error: unknown tool '$requested'. Expected claude or codex." >&2
        return 1
    fi
    echo "$match"
}

existing_tools() {
    local tool
    for tool in "${TOOLS[@]}"; do
        case "$tool" in
            claude) [ -d "$HOME/.claude" ] && echo "$tool" ;;
            codex) [ -d "$HOME/.codex" ] && echo "$tool" ;;
        esac
    done
}

link_path() {
    echo "$TOOL_DIR/$LINK_NAME"
}

alias_path() {
    echo "$TOOL_DIR/${FILE_PREFIX}$1.json"
}

current_alias_path() {
    echo "$TOOL_DIR/${FILE_PREFIX}$1.cur.json"
}

# Echo the alias currently marked ".cur", or return 1 if none.
find_cur() {
    local f base
    for f in "$TOOL_DIR"/"${FILE_PREFIX}"*.cur.json; do
        [ -e "$f" ] || continue
        base="${f##*/}"
        base="${base#"$FILE_PREFIX"}"
        echo "${base%.cur.json}"
        return 0
    done
    return 1
}

clear_marker() {
    local f
    for f in "$TOOL_DIR"/"${FILE_PREFIX}"*.cur.json; do
        [ -e "$f" ] || continue
        mv -f "$f" "${f%.cur.json}.json"
    done
}

# If the tool replaced its symlink with a real file, preserve the refreshed
# credentials under the alias marked current.
heal_if_clobbered() {
    local link cur
    link="$(link_path)"
    if [ -e "$link" ] && [ ! -L "$link" ]; then
        if cur="$(find_cur)"; then
            mv -f "$link" "$(current_alias_path "$cur")"
            echo "Recovered refreshed $TOOL credentials into ${FILE_PREFIX}${cur}.cur.json"
        else
            echo "Error: $link is a regular file and no $TOOL account is marked current." >&2
            echo "Cannot determine which aliased file it belongs to; resolve manually." >&2
            exit 1
        fi
    fi
}

show_current() {
    local link tgt alias cur
    link="$(link_path)"
    if [ -L "$link" ]; then
        tgt="$(basename "$(readlink "$link")")"
        alias="${tgt#"$FILE_PREFIX"}"
        alias="${alias%.cur.json}"
        alias="${alias%.json}"
        echo "$TOOL: $alias"
    elif [ -e "$link" ]; then
        if cur="$(find_cur)"; then
            echo "$TOOL: $cur ($link is a plain file after token refresh)" >&2
        else
            echo "$TOOL: no current marker ($link is a plain file)" >&2
        fi
    else
        echo "$TOOL: no account selected" >&2
    fi
}

list_aliases() {
    local f base
    for f in "$TOOL_DIR"/"${FILE_PREFIX}"*.json; do
        [ -e "$f" ] || continue
        base="${f##*/}"
        base="${base#"$FILE_PREFIX"}"
        base="${base%.cur.json}"
        base="${base%.json}"
        [ "$f" = "$(link_path)" ] || echo "  $base"
    done | sort -u >&2
}

switch_account() {
    local alias="$1" plain current link
    plain="$(alias_path "$alias")"
    current="$(current_alias_path "$alias")"
    link="$(link_path)"

    if [ ! -f "$plain" ] && [ ! -f "$current" ]; then
        echo "Error: no $TOOL credentials file for alias '$alias'." >&2
        echo "Available aliases:" >&2
        list_aliases
        exit 1
    fi

    heal_if_clobbered
    clear_marker
    mv -f "$plain" "$current"
    ln -sfn "${FILE_PREFIX}${alias}.cur.json" "$link"
    echo "Switched $TOOL to account '$alias' ($LINK_NAME -> ${FILE_PREFIX}${alias}.cur.json)"
}

if [ "${1:-}" = "-h" ] || [ "${1:-}" = "--help" ]; then
    usage
    exit 0
fi

if [ $# -gt 2 ]; then
    usage
    exit 1
fi

mapfile -t existing < <(existing_tools)

case $# in
    0)
        if [ "${#existing[@]}" -eq 0 ]; then
            echo "No ~/.claude or ~/.codex directory exists." >&2
            exit 1
        fi
        for tool in "${existing[@]}"; do
            configure_tool "$tool"
            show_current
        done
        ;;
    1)
        if [ "${#existing[@]}" -eq 1 ]; then
            configure_tool "${existing[0]}"
            switch_account "$1"
        else
            selected_tool="$(match_tool "$1")" || exit 1
            configure_tool "$selected_tool"
            show_current
        fi
        ;;
    2)
        selected_tool="$(match_tool "$1")" || exit 1
        configure_tool "$selected_tool"
        switch_account "$2"
        ;;
esac