diff --git a/bin/coat b/bin/coat
index e38b558b..2b116a9b 100755
--- a/bin/coat
+++ b/bin/coat
@@ -11,6 +11,49 @@
 # @author Jerry Lee (oldratlee at gmail dot com)
 set -eEuo pipefail
 
+# NOTE: DO NOT declare var PROG as readonly in ONE line!
+PROG=$(basename -- "$0")
+readonly PROG
+readonly PROG_VERSION='2.x-dev'
+
+################################################################################
+# parse options
+################################################################################
+
+progVersion() {
+  printf '%s version: %s\n' "$PROG" "$PROG_VERSION"
+  printf 'cat executable: %s\n' "$(command -v cat)"
+  exit
+}
+
+usage() {
+  cat <<EOF
+Usage: $PROG [OPTION]... [FILE]...
+cat lines colorfully.
+
+Support options:
+  --help     display this help and exit
+  --version  output version information and exit
+All other options and arguments are delegated to command cat,
+more info see the help/man of command cat(e.g. cat --help).
+cat executable: $(command -v cat)
+EOF
+
+  exit
+}
+
+declare -a args=("$@")
+# check arguments in reverse, so last option wins.
+for ((idx = $# - 1; idx >= 0; --idx)); do
+  [ "${args[idx]}" = --help ] && usage
+  [ "${args[idx]}" = --version ] && progVersion
+done
+unset args idx
+
+################################################################################
+# biz logic
+################################################################################
+
 # if stdout is not a terminal, use `cat` directly.
 #   '-t' check: is a terminal?
 #   check isatty in bash https://stackoverflow.com/questions/10022323
diff --git a/bin/taoc b/bin/taoc
index adf7e663..4534365e 100755
--- a/bin/taoc
+++ b/bin/taoc
@@ -11,6 +11,49 @@
 # @author Jerry Lee (oldratlee at gmail dot com)
 set -eEuo pipefail
 
+# NOTE: DO NOT declare var PROG as readonly in ONE line!
+PROG=$(basename -- "$0")
+readonly PROG
+readonly PROG_VERSION='2.x-dev'
+
+################################################################################
+# parse options
+################################################################################
+
+progVersion() {
+  printf '%s version: %s\n' "$PROG" "$PROG_VERSION"
+  printf 'tac executable: %s\n' "$(command -v tac)"
+  exit
+}
+
+usage() {
+  cat <<EOF
+Usage: $PROG [OPTION]... [FILE]...
+tac lines colorfully.
+
+Support options:
+  --help     display this help and exit
+  --version  output version information and exit
+All other options and arguments are delegated to command tac,
+more info see the help/man of command tac(e.g. tac --help).
+tac executable: $(command -v tac)
+EOF
+
+  exit
+}
+
+declare -a args=("$@")
+# check arguments in reverse, so last option wins.
+for ((idx = $# - 1; idx >= 0; --idx)); do
+  [ "${args[idx]}" = --help ] && usage
+  [ "${args[idx]}" = --version ] && progVersion
+done
+unset args idx
+
+################################################################################
+# biz logic
+################################################################################
+
 # if stdout is not a terminal, use `tac` directly.
 #   '-t' check: is a terminal?
 #   check isatty in bash https://stackoverflow.com/questions/10022323
diff --git a/docs/shell.md b/docs/shell.md
index ff81c3ae..b64e217e 100644
--- a/docs/shell.md
+++ b/docs/shell.md
@@ -154,48 +154,26 @@ line2 of file2
 # 帮助信息
 #   可以看到本人机器上实现代理的`cat`/`tac`命令是GNU的实现。
 $ coat --help
-Usage: cat [OPTION]... [FILE]...
-Concatenate FILE(s) to standard output.
-
-With no FILE, or when FILE is -, read standard input.
-
-  -A, --show-all           equivalent to -vET
-  -b, --number-nonblank    number nonempty output lines, overrides -n
-  -e                       equivalent to -vE
-  -E, --show-ends          display $ at end of each line
-  -n, --number             number all output lines
-  -s, --squeeze-blank      suppress repeated empty output lines
-  -t                       equivalent to -vT
-  -T, --show-tabs          display TAB characters as ^I
-  -u                       (ignored)
-  -v, --show-nonprinting   use ^ and M- notation, except for LFD and TAB
-      --help     display this help and exit
-      --version  output version information and exit
-
-Examples:
-  cat f - g  Output f's contents, then standard input, then g's contents.
-  cat        Copy standard input to standard output.
-
-GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
-Full documentation at: <https://www.gnu.org/software/coreutils/cat>
-or available locally via: info '(coreutils) cat invocation'
+Usage: coat [OPTION]... [FILE]...
+cat lines colorfully.
 
-$ taoc --help
-Usage: tac [OPTION]... [FILE]...
-Write each FILE to standard output, last line first.
-
-With no FILE, or when FILE is -, read standard input.
+Support options:
+  --help     display this help and exit
+  --version  output version information and exit
+All other options and arguments are delegated to command cat,
+more info see the help/man of command cat(e.g. cat --help).
+cat executable: /usr/local/opt/coreutils/libexec/gnubin/cat
 
-Mandatory arguments to long options are mandatory for short options too.
-  -b, --before             attach the separator before instead of after
-  -r, --regex              interpret the separator as a regular expression
-  -s, --separator=STRING   use STRING as the separator instead of newline
-      --help        display this help and exit
-      --version     output version information and exit
-
-GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
-Full documentation <https://www.gnu.org/software/coreutils/tac>
-or available locally via: info '(coreutils) tac invocation'
+$ taoc --help
+Usage: taoc [OPTION]... [FILE]...
+tac lines colorfully.
+
+Support options:
+  --help     display this help and exit
+  --version  output version information and exit
+All other options and arguments are delegated to command tac,
+more info see the help/man of command tac(e.g. tac --help).
+tac executable: /usr/local/opt/coreutils/libexec/gnubin/tac
 ```
 
 注：上面示例中，没有彩色；在控制台上运行可以看出彩色效果，如下：