Software 1 - scanf(), getline(), and unix shell (3)

Administrivia

Practice Web Page - http://www.cs.tau.ac.il/~efif/courses/Software1_Summer_03

Calculating the sign

• using the sign of the previous element

  for (i = ...) { sign *= -1;

• using the modulus operator '%'

  sign = i % 2;

• using the bitwise and operator '&'

  sign = (i & 0x1) ? -1 : 1;

Input format conversion

• int scanf(const char *format, ...) - Read formatted data from stdin

  /* Finding the maximum of 2 given numbers */ #include int main() { int i,j; printf("please insert the first number : "); scanf("%d", &i); printf("please insert the second number : "); scanf("%d", &j); printf("the larger number is : %d\n", i > j? i : j); return 0; }

getline

#include <stdio.h>

/*! getline() reads one line from standard input and copies it to line array
 * (but no more than max chars).
 * It does not place the terminating \n in line array.
 * Returns line length, or 0 for empty line, or EOF for end-of-file.
 */
int getline(char line[], int max)
{
  int nch = 0;
  int c;
  max = max - 1;			/* leave room for '\0' */

  while ((c = getchar()) != EOF) {
    if (c == '\n')
      break;

    if (nch < max) {
      line[nch] = c;
      nch = nch + 1;
    }
  }

  if (c == EOF && nch == 0)
    return EOF;

  line[nch] = '\0';
  return nch;
}

Unix Shells

• A small set of processing programs together with a program made to "glue the parts together." On a UNIX system such a program is called the shell
  • in contrast with the core that contains time-sharing code, file access code and other system oriented code.
• used to issue commands, start processes, control jobs, redirect input and output, and other mundane things that you do on a modern computer.
• the shell is a pretty complete programming language.
• Different shels (sh, csh, ksh, bash, tcsh, zsh, rc)
• UNIX shell

csh - Unix shell

• job control
• aliasing
• interactive

Redirection

ls > out sort < out > out1 ls >& out1 # redirect both errors and output to 'out1' ls >> out1 ls -s | sort | tail -5

Variables

• set/unset variables - regular variables, list variables
• Special variables:
  • PATH
  • HOME
  • USER
  • status

demo script - sort, tail

#! /usr/bin/csh -f ls -s > out sort -n < out | tail -5 - rm -f out

status variable

• Using the value returned by the status variable.
• Script for checking if compilation succeeded:

  #! /usr/bin/csh -f # this is a remark line! # $* is equivalent to $argv - all the arguments that program receive gcc -Wall $* if ( $status == 0 ) then echo Compilation succeeded else echo Compilation failed! endif

Shell prompt

• Creating a distinguished prompt

  Nova 1%

  • The name of host, followed by space, followed by the command number, followed by the character '%' for normal user, or '#' for supperuser
  • hostname - show or set the system's host name

    hostname -f

Capitalizing first character

• Create a program capitalize

  #include <stdio.h> #include <ctype.h> int main() { int c; if ((c = getchar()) == EOF) return 0; putchar(toupper(c)); while ((c = getchar()) != EOF) putchar(c); }

• compile and link
• copy executable to ~/bin/ directory

Changing the csh prompt

• edit the ~/.cshrc file

  if ( $?prompt ) then if ( -o /bin/su ) then set prompt="`hostname -s | ~/bin/capitalize` \!# " else set prompt="`hostname -s | ~/bin/capitalize` \!% " endif endif