History

• Created by Bill Joy at U.C. Berkeley in the late 1970s.
• Used as interactive login shell and a shell script command processor.
• Command language interpreter incorporating:
  • History
  • Job control
  • Interactive file name and username completion
  • C-like syntax

Version

Two versions:

1. /bin/csh: The original BSD version of csh.
2. /bin/tcsh: An improved version of csh called tcsh.
   • On many systems csh is linked here.

Login

When you login the shell is started in your home directory and commands are read from .cshrc and .login

Functionality

• history: Command to view command history.
• alias mechanism to make transformations on commands.
• unalias to unalias commands.
• fg, bg, and ^Z work the same.
• source can be used to read commands into the current shell.

Command Line Arguments

Special Variables:

• $0: Name of the script

• $1, $2, ..., $9, ${10}, ${11}, ...: Parameter variables

• $*: All parameters

• $#argv: Number of arguments

• $arv[1], $arr[2], …: Parameter variables

  • Note: Array subscripts start at 1 in C, not 0.

• $argv[*]: All arguments

• $argv: All arguments

• $#argv: Number of arguments

• $argv[$#argv]: Last argument

Reading Input from User

$<: Reads a line from stdin up to but not including newline.

• You can split a string separated by spaces into an array with set string=( $string )

Example

#!/bin/csh
echo "Name: "
set name=$<
echo Greetings, $name

Basic Operators

Control Structures

if (expression) command
if (expression) command then
    command
endif
if (expression) command then
    command
else if (expression) then
else
    command
endif

Example

if ($#arv < 2) then
    echo "Too few arguments"
    exit
endif

File Queries

• -e file: File merely exists (may be protected)
• -r file: File exists and is readable,
• -w file: File is writeable
• -x file: File is executable
• -o file: File is owned
• -z file: File has size 0
• -f file: File is an ordinary file
• -d file: File is a directory

Arithmetic (@)

#!/bin/csh
if ( $#argv == 0 ) then
    echo -n "Enter time in minutes: "
    @ min = $<
else
    @ min = $1
endif
@ sec = $min * 60
echo “$min minutes is $sec seconds”

Switch Case

#!/bin/csh -f
# Script name: colors
echo -n "Which color do you like? "
set color = $<
switch ("$color")
case bl*:
    echo I feel $color
    echo The sky is $color
    breaksw
case red:
     # Is is red or is it yellow?
    case yellow:
    echo The sun is sometimes $color.
    breaksw
default:
    echo $color not one of the categories.
    breaksw
endsw

Looping Constructs

Predetermined Iterations:

• repeat
  • Format: repeat command number
    • Executes command number times.
  • Ex: repeat 100 echo "Hello"
• foreach

foreach name ( wordlist )
    commands
end

• wordlist: list of words, or multi-valued variable

Condition-based Iterations:

• while

while ( expression )
    commands
end

• use when number of iterations not known in advance

set list = ( one two three )
foreach word ( $list )
  echo $word
end

#! /bin/csh
@ var = 5
while ( $var > 0 )
  echo $var
  @ var --
end

Loop Control

• break
• continue

Quoting

• Command Substitution: `…`
• Double Quotes: "..."
  • Prevent breakup of string into words.
  • Disabled most wildcard characters and the single quote.
    • $ keeps meaning
    • ! history references keep meaning
• Single Quotes: '...'
  • Escapes everything except !

eval

eval: Evaluates string and executes the result.

Example

set x=23
set y=x
eval echo \$$y

Debugging

% csh –n scriptname

• Parse commands but do not execute them

% csh –v scriptname

• Display each line of the script before execution

% csh –x scriptname

• Displays each line of the script after variable substitutions and before execution

Note: Flags can also be added to shebang