Scripting Languages and CShell

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Scripting Languages and C-Shell
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What is a scripting language ?

• Script is a sequence of commands written as plain
  text and run by an interpreter (shell).
• Today some scripting languages have evolved
  into lightweight programming languages.
• Used for lightweight operations such as
  manipulation of files and prototyping.
• Examples
• Shell scripts
• Perl
• Javascript

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C-Shell

• Unix systems come with a variety of shells, e.g.
  Bourne (sh), Bash (bash), C (csh), TC (tcsh).
• Find your shell echo SHELL
• C shell startup files .login, .cshrc
• Has C-like syntax

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Some Shell Metacharacters

• - commnet
• quote multiple characters but allow
  substitution
• - dereference a shell variable
• - execute in background
• quote multiple characters
• - match zero or more characters
• ? match a single character
• insert wild cards 0-3,5
• - separate commands
• ! refer to event in the history list !!,!4
• - substitute a command
• - refer to a job 3

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Some useful c-shell commands

• head / tail returns first / last lines of a
  file
• echo print command
• sort used to sort strings in lexicographical
  order
• cat concatenate files and print
• grep find regular expressions in files
• find find files by criteria
• wc word count on files
• diff - find differences between files
• basename / dirname extract file / directory
  name from full path
• touch change file timestamp
• mail sending mail
• cp/mv copy/move files

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Redirection and pipes

• prog redirection file
• gt redirect stdout
• gtgt append stdout
• gt redirect stdout and stderr
• gtgt append stdout and stderr
• lt redirect stdin
• prog1 pipe prog2
• redirect stdout of prog1 to stdin of
  prog2
• same, with stdout and stderr

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Some environment variables

• home name of home directory
• path search path
• prompt shell prompt
• cwd current working directory
• term type of terminal
• history length of history recorded

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How to write a c-shell script

• Edit the code file (no mandatory extension)
• Make sure the first line in the file is
• !/bin/csh f
• Add executable permission
• chmod x filename

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• !/bin/csh f
• hello worlds
• echo Hello world

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C-Shell Syntax
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Defining/changing shell variables

• Variables local to current shell
• String set var1strval1varNstrvalN
• Numeric _at_ var1numval1varNnumvalN
• Global variables
• setenv var strval set and export
• var or var access value of var
• Examples
• set name Alon string var.
• set name lt input from user
• _at_ a 0 numeric var.
• set dir pwd command substitution

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Array variables

• Available for integers and strings
• Indexed starting from 1!!!
• Declaration set name (array elements)
• name number of elements in array
• namei access the ith element
• namei-j elements i to j.
• Examples
• set students (David Ron Idit)
• set fib (0 1 1 2 3)
• set fib (fib 5) append
• set size fib size6

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Passing arguments to scripts

• argv1argv9 are assigned the command line
  arguments
• argv or - total number of arguments
• argv or - values of all arguments
• argv0 or 0 name of script
• shift variable_name in case there are more
  than 9 arguments shifts words one position to
  the left in variable (argv is the default).

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• !/bin/csh f
• simple_example
• string variable
• set course soft1
• echo course
• array
• set names ( Danny Dina Eyal Ayelet Ori Neta )
• echo names
• echo names size of array
• echo names2 the second element
• echo names2- starting from the second
  element
• echo names-2 until the second element

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• numeric variables and expression evaluation
• _at_ num 17
• echo num
• _at_ num - 3
• echo num
• _at_ num 14
• echo num
• if we want to assign the value of a command to
  a variable
• set chars wc -l ./simple_example
• echo chars
• accessing program parameters
• echo The program name is 0, the first
  parameter is 1 and the second is 2
• echo The number of parameters \(not including
  program name\) is argv

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Loops

• foreach identifier (set)
• . . .
• end
• while (expression)
• . . .
• end
• Expression can include the usual C operators.
• break, continue as in C.

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Conditional statements

• if (expression) command
• if (expression) then
• then-command-list
• else if (expression) then
• then-command-list
• . . .
• else
• else-command-list
• endif

• switch (value)
• case value1
• breaksw
• . . .
• default
• endsw

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Testing files attributes

• if (-op file_name) then
• -r read access
• -w write access
• -x execute access
• -e existence
• -o ownership
• -f plain (non-dir.) file
• -d directory
• -l link

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• !/bin/csh f
• sum
• if (argv 0) then
• echo Usage 0 num1 num2 num3 ...
• exit 1
• endif
• _at_ sum 0
• foreach number (argv)
• _at_ sum number
• end
• echo The sum is sum
• _at_ average sum / argv

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• !/bin/csh -f
• sort_files
• if (argv 0) then
• echo USAGE 0 file_names_to_sort
• echo This command writes on the original files
  \!\!\!
• exit 1
• endif
• foreach file(argv)
• sort file gt file.tmp
• mv file.tmp file
• end

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• !/bin/csh -f
• Biggest_file
• INPUT Directory name
• OUTPUT The file with the biggest number of
  characters in the given directory
• if (argv 0) then
• echo USAGE 0 directory_name
• exit 1
• endif
• if (-d 1) then
• _at_ max 0
• foreach file(1/)
• if (-r file -f file) then
• set wc_out wc -c file
• if (wc_out1 gt max) then
• set biggest_file wc_out2
• _at_ max wc_out1

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• !/bin/csh -f
• Modulo3
• INPUT sequence of integer numbers separated by
  \n terminated by 0
• OUTPUT prints the value of each number modulo
  3
• set num lt
• while (num ! 0)
• _at_ modulo num 3
• switch (modulo)
• case 0
• echo 0
• breaksw
• case 1
• echo 1
• breaksw

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Retrieving returned values

• Returned values (by return, exit) are stored in
  status environment variable
• The script
• !/bin/csh -f
• ./prog
• if (status ! 0) then
• echo "Error occured!"
• endif
• runs prog (from current dir) and reports
• whether an error occurred.

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awk/gawk

• Useful utility for file manipulation
• Processes input line by line.
• Example gawk print 1 input
• For details see
• http//www.gnu.org/software/gawk/manual/

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• !/usr/bin/gawk -f
• BEGIN stud_num total high_stud_num
  total_high 0
• if (NF ! 3)
• print "error in line", FNR, "", 0
• next
• stud_num
• total 3
• if (3 gt 80)
• total_high 3
• high_stud_num
• END print "Number of students ", stud_num
• print "Avergae grade is ", total /
  stud_num

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• Running with input
• Ron 033453671 91
• Yael 034567832 73
• Ran 040478124 100
• Yoav 060381253 95
• Tal 045623141 78 90
• Output is
• error in line 5 Tal 045623141 78 90
• Number of students 4
• Avergae grade is 89.75
• Average of high grades is 95.3333