learnxinyminutes-docs/tcsh.html.markdown
Boris Verkhovskiy da7182cb2e
Some checks are pending
Trigger site build / deploy (push) Waiting to run
CI / lint (push) Waiting to run
Reclassify shells as languages (#5150)
2024-10-20 15:11:09 -07:00

791 lines
26 KiB
Markdown
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

---
language: tcsh
filename: LearnTCSH.csh
contributors:
- ["Nicholas Christopoulos", "https://github.com/nereusx"]
---
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
# The first line of the script is a shebang which tells the system how to execute
# the script: http://en.wikipedia.org/wiki/Shebang_(Unix)
# TCSH emulates the shebang on systems that 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 $echo_style
# Enable `echo` to support backslashed characters and `-n` option (no new line)
# This is the default for tcsh, but your distro may change it. Slackware has
# done so.
set echo_style = both
# Prints "Hello world"
echo Hello world
echo "Hello world"
echo 'Hello world'
echo `echo Hello world`
# This prints "twonlines" in one line
echo two\nlines
# Prints the two lines
echo "two\nlines"
echo 'two\nlines'
# --- Basic Syntax ------------------------------------------------------------
# A special character (including a blank or tab) may be prevented from having
# its special meaning by preceding it with a backslash `\`.
# This will display the last history commands
echo !!
# This will not
echo \!\!
# Single quotes prevent expanding special characters too, but some
# characters like `!` and backslash have higher priority
# `$` (variable value) will not expand
echo '$1 tip'
# `!` (history) will expand
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 the first command fails"
echo "Always executed" && echo "Only executed if the first command does NOT fail"
# Parenthesised commands are always executed in a subshell,
# example: creates 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 leaves 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 variables from the rest when it is 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 the indexed element; This 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 an 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` is useful for 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 filename 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 ( != $user ) ...
# which is invalid syntax
# The "safe" way to use potentially empty variables in tcsh is:
# if ( "$name" != $user ) ...
# which, when $name is empty, is seen by tcsh as:
# if ( "" != $user ) ...
# which works as expected
# There is also conditional execution
echo "Always executed" || echo "Only executed if the first command fails"
echo "Always executed" && echo "Only executed if the first command does NOT fail"
# To use && and || with if statements, you don't need multiple pairs of
# square brackets:
if ( "$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 parenthesized
# !, ~, |, &, ^, ~, <<, >>,
# Compare and logical operators
#
# All operators are the 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 it works well when
# the expression is parenthesized, otherwise the primary parser seems to be
# active. Parentheses 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 ++
# No shell was 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 the second option
# (https://www.gnu.org/software/bc/manual/html_mono/bc.html)
#
# The standard Unix's AWK as the third option
# (https://www.gnu.org/software/gawk/manual/gawk.html)
# You can also use `Perl`, `PHP`, `python`, 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 built-in `filetest` command does 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, display a message
if ( -e README ) echo "I have already README file"
# If the `less` program is installed, use it 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 last access time (atime) -A: returns atime string
# -U returns the owner's user ID -U: returns the owner's user name
# -G returns the owner's group ID -G: returns the owner's group name
# -P returns the permissions as octal number -Pmode returns perm. AND mode
# this will display the date as a 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 through the filesystem with `chdir` (cd)
cd path # change working directory
cd # change to the home directory
cd - # change to the 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. These `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 Unix programs and they have their
# own man-page. The `pipe` mechanism is part of the kernel but the syntax
# and the control is the shell's job, the tcsh in our case.
# NOTE: Windows has the `pipe` mechanism too, but it is buggy and I signed it
# for all versions until Windows XP SP3 API32 which was the last one that I
# worked on. Microsoft denied it, but it is a 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 the 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 Unixes. The `ps2pdf`
# program is part of the `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 to true, then the command is executed.
# `command` must be a simple command, not an alias, a pipeline, a command list
#, or a parenthesized command list. With a few words, avoid using it.
#
# BUG: Input/output redirection occurs even if expr is false and the command
# is thus not executed.
#
# check if we are in a 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 it's 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 jumps 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 'parameters =' $params
#### REPEAT
# Syntax: repeat count command
#
# The specified command, which is subject to the same restrictions as the
# command in the one line `if` statement above, is executed count times.
# I/O redirections occur exactly once, even if `count` is 0.
#
# TIP: in most cases prefer `while`
repeat 3 echo "ding dong"
# --- Functions ---------------------------------------------------------------
# tcsh has no functions but its expression syntax is advanced enough to use
# `alias` as functions. Another method is recursion
# Alias argument selectors; the ability to define an alias to take arguments
# supplied to it and apply them to the commands that it refers to.
# Tcsh is the only shell that provides this feature.
#
# \!# argument selector for all arguments, including the alias/command
# itself; arguments need not be supplied.
# \!* argument selector for all arguments, excluding the alias/command;
# arguments need not be supplied.
# \!$ 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 sets 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 for its bugs;
# * It is also famous for its advanced interactive mode.
# * TCSH is famous for having the most advanced completion subsystem.
# * TCSH is famous for having the most advanced aliases subsystem; aliases
# can take parameters and often be used as functions!
# * TCSH is well known and preferred by people (me too) because of better
# syntax. All shells are using Thomson's syntax with the exception of
# [t]csh, fish, and plan9's shells (rc, ex).
# * It is smaller and consumes far less memory than bash, zsh, and even mksh!
# (memusage reports)
# * TCSH still has bugs; fewer, but it does; if you write readable clean code
# you'll find none; well almost none... This has to do with the implementation
# of csh; that doesn't mean the other shells have a good implementation.
# * no well-known shell is capable of regular programming; if your script
# is getting big, use a programming language, like Python, PHP, or Perl (good
# scripting languages).
#
# Advice:
# 1. Do not use redirection in single-line IFs (it is well documented bug)
# In most cases avoid using 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` and `set x = 1` worked, but `set x =1` did not!
# 4. It is well documented that numeric expressions require spaces in between;
# also parenthesize 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 a 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 that were written without it.
#
# NOTE: The same for `parseoctal`, but it is better to fix the problematic
# scripts.
#
# NOTE: **for beginners only**
# This enables automatic rescanning of `path` directories if needed. (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 %# "
```