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+---
+language: tcsh
+filename: LearnTCSH.csh
+contributors:
+    - ["Nicholas Christopoulos", "https://github.com/nereusx"]
+lang: en
+---
+tcsh ("tee-see-shell") is a Unix shell based on and compatible with the C shell (csh).
+It is essentially the C shell with programmable command-line completion, command-line editing,
+and a few other features.
+It is the native root shell for BSD-based systems such as FreeBSD.
+
+Almost all Linux distros and BSD today use tcsh instead of the original csh. In
+most cases csh is a symbolic link that points to tcsh.
+This is because tcsh is backward compatible with csh, and the last
+is not maintained anymore.
+
+- [TCSH Home](http://www.tcsh.org/)
+- [TCSH Wikipedia](https://en.wikipedia.org/wiki/Tcsh)
+- [TCSH manual page](http://www.tcsh.org/tcsh.html/top.html)
+- [“An Introduction to the C shell”, William Joy](https://docs.freebsd.org/44doc/usd/04.csh/paper.html)
+- [TCSH Bug reports and/or features requests](https://bugs.gw.com/)
+
+Some more files:
+[tcsh help command (for 132x35 terminal size)](https://github.com/nereusx/dotfiles/blob/master/csh-help),
+[my ~/.tcshrc](https://github.com/nereusx/dotfiles/blob/master/.tcshrc)
+
+```tcsh
+#!/bin/tcsh
+# First line of the script is shebang which tells the system how to execute the
+# script: http://en.wikipedia.org/wiki/Shebang_(Unix)
+# TCSH emulates the shebang on systems which don't understand it.
+
+# In most cases you'll use `#!/bin/tcsh -f', because `-f' option does not load
+# any resource or start-up files, or perform any command hashing, and thus
+# starts faster.
+
+# --- the echo command --------------------------------------------------------
+# The `echo' writes each word to the shell's standard output, separated by
+# spaces and terminated with a newline. The echo_style shell variable may be
+# set to emulate (or not) the flags and escape sequences.
+
+# Display the value of echo_style
+echo $echo_style
+
+# Enable `echo' to support backslashed characters and `-n' option (no new line)
+# This is the default for tcsh, but your distro may change it. Slackware has
+# done so.
+set echo_style = both
+
+# Prints "Hello world"
+echo Hello world
+echo "Hello world"
+echo 'Hello world'
+echo `echo Hello world`
+
+# This prints "twonlines" in one line
+echo two\nlines
+
+# Prints the two lines
+echo "two\nlines"
+echo 'two\nlines'
+
+# --- Basic Syntax ------------------------------------------------------------
+
+# A special character (including a blank or tab) may be prevented from having
+# its special meaning by preceding it with a backslash `\'.
+# this will display the last history commands
+echo !!
+# this will not
+echo \!\!
+
+# Single quotes prevents expanding special characters too, but some
+# characters like `!' and backslash have higher priority
+# `$' (variable value) will not expands
+echo '$1 tip'
+# `!' (history) will expands
+echo '!!'
+
+# Strings enclosed by back-quotes will be executed and replaced by the result.
+echo `ls`
+
+# Semi-colon separate commands
+echo 'first line'; echo 'second line'
+
+# There is also conditional execution
+echo "Always executed" || echo "Only executed if first command fails"
+echo "Always executed" && echo "Only executed if first command does NOT fail"
+
+# Parenthesised commands are always executed in a subshell,
+
+# example: create a project and then informs you that it finished while
+# it does the installation.
+make && ( espeak "BOSS, compilation finished"; make install )
+
+# prints the home directory but leaving you where you were
+(cd; pwd); pwd
+
+# Read tcsh man-page documentation
+man tcsh
+
+# --- Variables ---------------------------------------------------------------
+# The shell maintains a list of variables, each of which has as value a list of
+# zero or more words. The values of shell variables can be displayed and
+# changed with the `set' and `unset' commands.
+# The system maintains its own list of ``environment'' variables.
+# These can be displayed and changed with `printenv', `setenv' and `unsetenv'.
+# The syntax of setenv is similar to POSIX sh.
+
+# Assign a value or nothing will create a variable
+# Assign nothing
+set var
+# Assign a numeric value
+# the '@' denotes the expression is arithmetic; it works similar to 'set' but
+# the right value can be a numeric expression.
+@ var = 1 + 2
+# Assign a string value
+set var = "Hello, I am the contents of 'var' variable"
+# Assign the output of a program
+set var = `ls`
+
+# Remove a variable
+unset var
+# Prints 1 (true) if the variable `var' exists otherwise prints 0 (false)
+echo $?var
+# Print all variables and their values
+set
+
+# Prints the contents of 'var'
+echo $var;
+echo "$var";
+# Prints the string `$var'
+echo \$var
+echo '$var'
+# braces can be used to separate variable from the rest when its needed
+set num = 12; echo "There ${num}th element"
+
+# Prints the number of characters of the value: 6
+set var = '123456'; echo $%var
+
+### LISTs
+# Assign a list of values
+set var = ( one two three four five )
+# Print all the elements: one two three four five
+echo $var
+echo $var[*]
+# Print the count of elements: 5
+echo $#var
+# Print indexed element; prints the second element: two
+echo $var[2]
+# Print range of elements; prints 2nd up to 3rd: two, three
+echo $var[2-3]
+# Prints all elements starting from the 3rd: three four five
+echo $var[3-]
+# Prints print all up to 3rd element: one two three
+echo $var[-3]
+
+### Special Variables
+# $argv         list of command-line arguments
+# $argv[0]      this file-name (the file of the script file)
+# $# $0, $n, $* are the same as $#argv, $argv[0], $argv[n], $argv[*]
+# $status, $?   the exit code of the last command that executed
+# $_            the previous command line
+# $!            the PID of the last background process started by this shell
+# $$            script's PID
+
+# $path, $PATH  the list of directories that will search for executable to run
+# $home, $HOME  user's home directory, also the `~' can be used instead
+# $uid          user's login ID
+# $user         user's login name
+# $gid          the user's group ID
+# $group        the user's group-name
+# $cwd, $PWD    the Current/Print Working Directory
+# $owd          the previous working directory
+# $tcsh         tcsh version
+# $tty          the current tty; ttyN for linux console, pts/N for terminal
+#               emulators under X
+# $term         the terminal type
+# $verbose      if set, causes the words of each command to be printed.
+#               can be set by the `-v' command line option too.
+# $loginsh      if set, it is a login shell
+
+# TIP: $?0 is always false in interactive shells
+# TIP: $?prompt is always false in non-interactive shells
+# TIP: if `$?tcsh' is unset; you run the original `csh' or something else;
+#      try `echo $shell'
+# TIP: $verbose this is useful to debugging scripts
+# NOTE: $PWD and $PATH are synchronised with $cwd and $pwd automatically.
+
+# --- Variable modifiers ------------------------------------------------------
+# Syntax: ${var}:m[:mN]
+# Where <m> is:
+# h : the directory  t : the filenane  r : remove extension   e : the extension
+# u : uppercase the first lowercase letter
+# l : lowercase the first uppercase letter
+# p : print but do not execute it (hist)
+# q : quote the substituted words, preventing further substitutions
+# x : like q, but break into words at white spaces
+# g : apply the following modifier once to each word
+# a  : apply the following modifier as many times as possible to single word
+# s/l/r/ : search for `l' and replace with `r', not regex; the `&' in the r is
+# replaced by l
+# & : Repeat the previous substitution
+
+# start with this file
+set f = ~/Documents/Alpha/beta.txt
+# prints ~/Documents/Alpha/beta
+echo $f:r
+# prints ~/Documents/Alpha
+echo $f:h
+# prints beta.txt
+echo $f:t
+# prints txt
+echo $f:e
+# prints beta
+echo $f:t:r
+# prints Beta
+echo $f:t:r:u
+# prints Biota
+echo $f:t:r:u:s/eta/iota/
+
+# --- Redirection -------------------------------------------------------------
+
+# Create file.txt and write the standard output to it
+echo 'this string' > file.txt
+# Create file.txt and write the standard output and standard error to it
+echo 'this string' >& file.txt
+# Append the standard output to file.txt
+echo 'this string' >> file.txt
+# Append the standard output and standard error to file.txt
+echo 'this string' >>& file.txt
+# Redirect the standard input from file.txt
+cat < file.txt
+# Input from keyboard; this stores the input line to variable `x'
+set x = $<
+# Document here;
+cat << LABEL
+...text here...
+LABEL
+
+# TIP: this is how to get standard error separated:
+(grep 'AGP' /usr/src/linux/Documentation/* > output-file.txt) >& error-file.txt
+
+# example: read a name from standard input and display a greetings message
+echo -n "Enter your name? "
+set name = $<
+echo "Greetings $name"
+
+# --- Expressions ------------------------------------------------------------
+
+# Operators:
+# ==  equal         !=  not equal    !  not
+#  >  greater than   <  less than   >=  greater or equal  <= less or equal
+# &&  logical AND   ||  logical OR
+
+if ( $name != $user ) then
+    echo "Your name isn't your username"
+else
+    echo "Your name is your username"
+endif
+
+# single-line form
+if ( $name != $user ) echo "Your name isn't your username"
+
+# NOTE: if $name is empty, tcsh sees the above condition as:
+# if ( != $user ) ...
+# which is invalid syntax
+# so the "safe" way to use potentially empty variables in tcsh is:
+# if ( "$name" != $user ) ...
+# which, when $name is empty, is seen by tcsh as:
+# if ( "" != $user ) ...
+# which works as expected
+
+# There is also conditional execution
+echo "Always executed" || echo "Only executed if first command fails"
+echo "Always executed" && echo "Only executed if first command does NOT fail"
+
+# To use && and || with if statements, you don't need multiple pairs of
+# square brackets:
+if ( "$name" == "Steve" && "$age" == 15 ) then
+    echo "This will run if $name is Steve AND $age is 15."
+endif
+
+if ( "$name" == "Daniya" || "$name" == "Zach" ) then
+    echo "This will run if $name is Daniya OR Zach."
+endif
+
+# String matching operators ( `=~' and `!~' )
+# The ‘==’ ‘!=’ ‘=~’ and ‘!~’ operators compare their arguments as strings;
+# all others operate on numbers. The operators ‘=~’ and ‘!~’ are like ‘!=’
+# and ‘==’ except that the right hand side is a glob-pattern against which
+# the left hand operand is matched.
+
+if ( $user =~ ni[ck]* ) echo "Greetings Mr. Nicholas."
+if ( $user !~ ni[ck]* ) echo "Hey, get out of Nicholas PC."
+
+# Arithmetic expressions are denoted with the following format:
+@ result = 10 + 5
+echo $result
+
+# Arithmetic Operators
+# +, -, *, /, %
+#
+# Arithmetic Operators which must be parenthesised
+# !, ~, |, &, ^, ~, <<, >>,
+# Compare and logical operators
+#
+# All operators are same as in C.
+
+# It is non so well documented that numeric expressions require spaces
+# in-between; Also, `@' has its own parser, it seems that work well when the
+# expression is parenthesised otherwise the primary parser seems it is active.
+# Parenthesis require spaces around, this is documented.
+
+# wrong
+@ x = $y+1
+@ x = 0644 & 022;      echo $x
+@ x = (0644 & 022) +1; echo $x
+@ x = (0644 & 022)+ 1; echo $x
+@ x = ( ~077 );        echo $x
+
+# correct
+@ x = $y + 1
+@ x = ( 0644 & 022 ) + 1; echo $x
+@ x = ( ~ 077 );          echo $x
+@ x = ( ~ 077 | 022 );    echo $x
+@ x = ( ! 0 );            echo $x
+
+# C's operators ++ and -- are supported if there is not assignment
+@ result ++
+
+# None shell created to do mathematics;
+# Except for the basic operations, use an external command with backslashes.
+#
+# I suggest the calc as the best option.
+# (http://www.isthe.com/chongo/tech/comp/calc/)
+#
+# The standard Unix's bc as second option
+# (https://www.gnu.org/software/bc/manual/html_mono/bc.html)
+#
+# The standard Unix's AWK as third option
+# (https://www.gnu.org/software/gawk/manual/gawk.html)
+
+# You can also use `perl', `php' or even several BASICs, but prefer the
+# above utilities for faster load-and-run results.
+
+# real example: (that I answer in StackExchange)
+# REQ: x := 1001b OR 0110b
+
+# in `tcsh' expression (by using octal)
+@ x = ( 011 | 06 ); echo $x
+
+# the same by using `calc' (and using binary as the original req)
+set x = `calc '0b1001 | 0b110'`; echo $x
+
+# --- File Inquiry Operators --------------------------------------------------
+# NOTE: The builtin `filetest' command do the same thing.
+
+#### Boolean operators
+# -r  read access    -w  write access    -x  execute access    -e  existence
+# -f  plain file     -d  directory       -l  symbolic link     -p  named pipe
+# -S  socket file
+# -o  ownership      -z  zero size       -s  non-zero size
+# -u  SUID is set    -g  SGID is set     -k  sticky is set
+# -b  block device   -c  char device
+# -t  file (digit) is an open file descriptor for a terminal device
+
+# if the file `README' exists, displays a message
+if ( -e README ) echo "I have already README file"
+
+# if the `less' program is installed, use this instead of `more'
+if ( -e `where less` ) then
+	alias more 'less'
+endif
+
+#### Non-boolean operators
+# -Z  returns the file size in bytes
+# -M  returns the modification time (mtime)    -M: returns mtime string
+# -A  returns the lass access time (atime)     -A: returns atime string
+# -U  returns the owners user ID               -U: returns the owners user-name
+# -G  returns the group ID                     -G: returns the group-name
+# -P  returns the permissions as octal number  -Pmode returns perm. AND mode
+
+# this will display the date as Unix-time integer: 1498511486
+filetest -M README.md
+
+# This will display "Tue Jun 27 00:11:26 2017"
+filetest -M: README.md
+
+# --- Basic Commands ----------------------------------------------------------
+
+# Navigate though file system with `chdir' (cd)
+cd path # change working directory
+cd      # change to home directory
+cd -    # change to previous directory
+cd ..   # go up one directory
+
+# Examples:
+cd ~/Downloads # go to my `Downloads' directory
+
+# Use `mkdir` to create new directories.
+mkdir newdir
+# The `-p` flag causes new intermediate directories to be created as necessary.
+mkdir -p ~/.backup/saves
+
+# which & where
+# find if csh points to tcsh
+ls -lha `which csh`
+# find if csh is installed on more than one directory
+where csh
+
+# --- Pipe-lines --------------------------------------------------------------
+# A pipeline is a sequence of processes chained together by their standard
+# streams, so that the output of each process (stdout) feeds directly as input
+# (stdin) to the next one. This `pipes' are created with the `|' special
+# character and it is one of the most powerful characteristics of Unix.
+
+# example:
+ls -l | grep key | less
+# "ls -l" produces a process, the output (stdout) of which is piped to the
+# input (stdin) of the process for "grep key"; and likewise for the process
+# for "less".
+
+# the `ls', the `grep' and the `less' are programs of Unix and they have their
+# own man-page. The `pipe' mechanism is part of the kernel but the syntax
+# and the control is job of the shell, the tcsh in our case.
+
+# NOTE: `pipe' mechanism has Windows too, but it is buggy and I sign it for all
+# versions until Windows XP SP3 API32 which was the last one that I worked on.
+# Microsoft still denied it but is well known bug since it is a common method
+# for inter-process communication. For small I/O it will work well.
+# tcsh, along with grep, gcc and perl is one of the first Unix programs that
+# ported to DOS (with EMX DOS extender) and later to Windows (1998).
+
+# example: this will convert tcsh to PostScript and will show it with okular
+zcat /usr/man/man1/tcsh.1.gz | groff -Tps -man | okular -
+
+# a better version
+zcat `locate -b -n 1 '\tcsh.1.gz'` | groff -Tps -man | okular -
+
+# even better
+set page = tcsh; set loc = (locate -b -n 1 "\\\\"${page}".1.gz");
+ zcat `eval $loc` | groff -Tps -man | okular -
+
+# the same, modified to create man page pdf
+set page = tcsh; set loc = (locate -b -n 1 "\\\\"${page}".1.gz");
+ zcat `eval $loc` | groff -Tps -man | ps2pdf - ${page}.pdf
+
+# the same, but now shows the ${page}.pdf too
+set page = tcsh; set loc = (locate -b -n 1 "\\\\"${page}".1.gz");
+ zcat `eval $loc` | groff -Tps -man | ps2pdf - ${page}.pdf && okular tcsh.pdf
+
+# NOTE: `okular' is the default application of KDE environment and it shows
+# postcript and pdf files. You can replace it with your lovely pdf viewer.
+# zcat, locate, groff, are common programs in all Unices. `ps2pdf' program
+# is part of `ghostscript' package that is widely used.
+
+# --- Control Flow ------------------------------------------------------------
+
+#### IF-THEN-ELSE-ENDIF
+# Syntax:
+# if ( expr ) then
+#    ...
+# [else if ( expr2 ) then
+#    ...]
+# [else
+#    ...]
+# endif
+#
+# If the specified expr is true then the commands to the first else are
+# executed; otherwise if expr2 is true then the commands to the second else
+# are executed, etc.
+# Any number of else-if pairs are possible; only one endif is needed.
+#
+# Single-line form:
+#
+# if ( expr ) command
+#
+# If `expr' evaluates true, then command is executed.
+# `command' must be a simple command, not an alias, a pipeline, a command list
+# or a parenthesized command list. With few words, avoid to use it.
+#
+# BUG: Input/output redirection occurs even if expr is false and command is
+# thus not executed.
+#
+
+# check if we are in non-interactive shell and quit if true
+if ( $?USER == 0 || $?prompt == 0 ) exit
+
+# check if we are a login shell
+if ( $?loginsh ) then
+	# check if you are on linux console (not X's terminal)
+	if ( $tty =~ tty* ) then
+		# enable keypad application keys (man console_codes)
+		echo '\033='
+	endif
+endif
+
+#### SWITCH-ENDSW
+# Syntax:
+# switch ( expr )
+# case pattern:
+#     ...
+#     [breaksw]
+# [default:
+#     ...]
+# endsw
+#
+# tcsh uses a case statement that works similarly to switch in C.
+# Each case label is successively matched, against the specified string which
+# is first command and filename  expanded. The file  metacharacters `*', `?'
+# and `[...]' may be used in the case labels. If none of the labels match the
+# execution begins after the default label if its defined.
+# The command `breaksw' causes execution to continue after the endsw. Otherwise
+# control may fall through case labels and default labels as in C.
+
+switch ( $var )
+case *.[1-9]:
+case *.[1-9].gz:
+	echo "$var is a man-page."
+	breaksw
+case *gz:
+	echo "$var is gzipped"
+	breaksw
+default:
+	file $var
+endsw
+
+#### FOREACH-END
+# Syntax:
+# foreach name ( wordlist )
+#	...
+#   [break | continue]
+# end
+#
+# Successively sets the variable `name' to each member of `wordlist' and
+# executes the sequence of commands between this command and the matching
+# `end' keyword. The `continue' keyword jump to the next element back to
+# top; and the `break' keyword terminates the loop.
+#
+# BUG: `foreach' doesn't ignore here documents when looking for its end.
+
+# example: counting 1 to 10
+foreach i ( `seq 1 10` )
+    echo $i
+end
+
+# example: type all files in the list
+foreach f ( a.txt b.txt c.txt )
+	cat $f
+end
+
+# example: convert wma to ogg
+foreach f ( *.wma )
+	ffmpeg -i "$f" "$f:r".ogg
+end
+
+#### WHILE-END
+# while ( expr )
+#     ...
+#     [break | continue]
+# end
+#
+# Executes the commands between the `while' and the matching `end' while `expr'
+# evaluates non-zero. `break' and `continue' may be used to terminate or
+# continue the loop prematurely.
+
+# count from 1 to 10
+set num = 1
+while ( $num <= 10 )
+	echo $num
+	@ num ++
+end
+
+# print all directories of CWD
+set lst = ( * )
+while ( $#lst )
+	if ( -d $lst[1] ) echo $lst[1] is directory
+	shift lst
+end
+
+# separate command-line arguments to options or parameters
+set options
+set params
+set lst = ( $* )
+while ( $#lst )
+	if ( "$lst[1]" =~ '-*' ) then
+		set options = ( $options $lst[1] )
+	else
+		set params = ( $params $lst[1] )
+	endif
+	shift lst
+end
+echo 'options =' $options
+echo 'paramaters =' $params
+
+#### REPEAT
+# Syntax: repeat count command
+#
+# The specified command, which is subject to the same restrictions as the
+# command in the one line if statement above, is executed count times.
+# I/O redirections occur exactly once, even if count is 0.
+#
+# TIP: in most cases prefer `while'
+
+repeat 3 echo "ding dong"
+
+# --- Functions ---------------------------------------------------------------
+# tcsh has no functions but its expression syntax is advanced enough to use
+# `alias' as functions. Another method is recursion
+
+# Alias argument selectors; the ability to define an alias to take arguments
+# supplied to it and apply them to the commands that it refers to.
+# Tcsh is the only shell that provides this feature.
+#
+# \!#   argument selector for all arguments, including the alias/command
+#       itself; arguments need not be supplied.
+# \!*   argument selector for all arguments, excluding the alias/command;
+#       arguments need not be supplied.
+# \!$   argument selector for the last argument; argument need not be supplied,
+#       but if none is supplied, the alias name is considered to be the
+#       last argument.
+# \!^   argument selector for first argument; argument MUST be supplied.
+# \!:n  argument selector for the nth argument; argument MUST be supplied;
+#       n=0 refers to the alias/command name.
+# \!:m-n   argument selector for the arguments from the mth to the nth;
+#       arguments MUST be supplied.
+# \!:n-$   argument selector for the arguments from the nth to the last;
+#       at least argument n MUST be supplied.
+
+# Alias the cd command so that when you change directories, the contents
+# are immediately displayed.
+alias cd 'cd \!* && ls'
+
+# --- Recursion method --- begin ---
+#!/bin/tcsh -f
+set todo = option1
+if ( $#argv > 0 ) then
+	set todo = $argv[1]
+endif
+
+switch ( $todo )
+case option1:
+#	...
+	$0 results
+	breaksw
+case option2:
+#	...
+	$0 results
+	breaksw
+case results:
+	echo "print the results here"
+#	...
+	breaksw
+default:
+	echo "Unknown option: $todo"
+#	exit 0
+endsw
+# --- Recursion method --- end ---
+
+# --- examples ----------------------------------------------------------------
+
+# this script prints available power-states if no argument is set;
+# otherwise it set the state of the $argv[1]
+# --- power-state script --- begin --------------------------------------------
+#!/bin/tcsh -f
+# get parameter ("help" for none)
+set todo = help
+if ( $#argv > 0 ) then
+	set todo = $argv[1]
+endif
+# available options
+set opts = `cat /sys/power/state`
+# is known?
+foreach o ( $opts )
+	if ( $todo == $o ) then
+		# found; execute it
+		echo -n $todo > /sys/power/state
+		break
+	endif
+end
+# print help and exit
+echo "usage: $0 [option]"
+echo "available options on kernel: $opts"
+# --- power-state script --- end ----------------------------------------------
+
+# Guess the secret number game
+# --- secretnum.csh --- begin -------------------------------------------------
+#!/bin/tcsh -f
+set secret=`shuf -i1-100 -n1`
+echo "I have a secret number from 1 up to 100"
+while ( 1 )
+	echo -n "Guess: "
+	set guess = $<
+	if ( $secret == $guess ) then
+		echo "You found it"
+		exit 1
+	else
+		if ( $secret > $guess ) then
+			echo "its greater"
+		else if ( $secret < $guess ) then
+				echo "its lesser"
+			endif
+		endif
+	endif
+end
+# --- secretnum.csh --- end ---------------------------------------------------
+
+# -----------------------------------------------------------------------------
+# Appendices
+
+#### About [T]CSH:
+# * CSH is notorious about its bugs;
+# * It was also famous about its advanced interactive mode.
+# * TCSH is famous that have the most advanced completition subsystem.
+# * TCSH is famous that have the most advanced aliases subsystem; aliases
+#   can take parameters and often used as functions!
+# * TCSH is well known that preferred by people  (me too) because of better
+#   syntax. All shells are using Thomson's syntax with exception of [t]csh,
+#   fish and plan9's shells (rc, ex).
+# * It is smaller and consume far less memory than bash, zsh even mksh!
+#   (memusage reports)
+# * TCSH still has bugs; less but have; if you write readable clean code you'll
+#   find none; well almost none... This has to do with the implementation of
+#   csh; that no means the other shells has good implementation.
+# * no one well known shell is capable for regular programming; if your script
+#   getting big, use a programming language, or at least PHP or Perl (good
+#   script languages).
+#
+# Advises:
+# 1. Do not use redirection in single-line if (it is well documented bug)
+#    In most cases avoid to use single-line IFs.
+# 2. Do not mess up with other shells code, c-shell is not compatible with
+#    other shells and has different abilities and priorities.
+# 3. Use spaces as you'll use them to write readable code in any language.
+#    A bug of csh was `set x=1' worked, `set x = 1' worked, `set x =1' did not!
+# 4. It is well documented that numeric expressions require spaces in-between;
+#    also parenthesise all bit-wise and unary operators.
+# 5. Do not write a huge weird expression with several quotes, backslashes etc
+#    It is bad practice for generic programming, it is dangerous in any shell.
+# 6. Help tcsh, report the bug here <https://bugs.gw.com/>
+# 7. Read the man page, `tcsh' has huge number of options, and variables.
+#
+#    I suggest the following options enabled by default
+#    --------------------------------------------------
+# Even in non-interactive shells
+#    set echo_style=both
+#    set backslash_quote
+#    set parseoctal
+#    unset noclobber
+#
+# Whatever...
+#    set inputmode=insert
+#    set autolist
+#    set listjobs
+#    set padhour
+#    set color
+#    set colorcat
+#    set nobeep
+#    set cdtohome
+#
+#    set histdup
+#    set histlit
+#    set nohistclop
+#
+#    unset compat_expr
+#    unset noglob
+#    unset autologout
+#    unset time
+#    unset tperiod
+#
+# NOTE: If the `backslash_quote' is set, it may create compatibility issues
+# with other tcsh scripts which was written without it.
+#
+# NOTE: The same for `parseoctal', but it is better to fix the problematic
+# scripts.
+#
+# NOTE: **for beginners only**
+# This enable automatically rescan `path' directories if need to. (like bash)
+#    set autorehash
+
+#### common aliases
+#    alias hist  'history 20'
+#    alias ll    'ls --color -lha'
+#    alias today "date '+%d%h%y'
+#    alias ff    'find . -name '
+
+#### a nice prompt
+#    set prompt = "%B%{\033[35m%}%t %{\033[32m%}%n@%m%b %C4 %# "
+```