More UNIX Commands

File Information

Some useful UNIX file utilities:

• wc counts the lines, words and characters in a text file.

  Example: executing

  wc pub/swap.c
  

  in my home directory produces:

        30      92     537 pub/swap.c
  

  Example: executing

  wc pub/*.c
  

  in my home directory produces a count of lines, words and characters for each file ending in .c in my pub subdirectory.
• grep searches for occurrences of a word or string in a file. It returns each line of the file containing the word.

  Format:

  grep pattern file

  Example: executing

   grep val1 swap.c
  

  in my pub subdirectory finds all lines containing val1 in file swap.c, producing:

    int val1 = 3, val2 = 10;
    printf("The value of val1 is %d\n", val1);
    swap(&val1, &val2);
    printf("The value of val1 is %d\n", val1);
  

  Example: executing

   grep temp *.c
  

  in my pub subdirectory finds all lines containing temp in all files ending in .c, producing:

  array4.c:  float temp;
  array4.c:  temp = cgs[i];
  array4.c:  cgs[j] = temp;
  array4.c:  float temp;
  array4.c:  temp = *i;
  array4.c:  *j = temp;
  cellFahr.c:  printf("Enter the celsius temperature: ");
  prog6.c:  bookrec temp;
  prog6.c:  temp = *i;
  prog6.c:  *j = temp;
  swap.c:  int temp;
  swap.c:  temp = *i;
  swap.c:  *j = temp;
  

  Note that each line of output is labeled with the file it came from.
• sort produces a sorted version of a file. If file atextfile contains:

  this is
  a text
  file
  by me.
  

  then

  sort atextfile
  

  produces:

  a text
  by me.
  file
  this is
  

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Other Information

Some useful commands:

• who shows everyone who is logged into the system and gives some information about what they are doing.
• finger gives information about particular users:
  • finger with no parameters is similar to who
  • finger userid gives information about user userid. Helpful for checking if someone is logged in. Also displays the contents of file .plan in that user's home directory if permissions are set appropriately.
  • finger userid@host gives information about user userid of system host if that system responds to finger requests.
• date prints the current date and time according to the system clock
• cal prints a calender for the current month. cal interprets one parameter as a year to print a calender for, and two as a month and year to print a calendar for.

UNIX commands can also be executed from inside C programs by calling the system() function whose prototype is in stdlib.h.

Example:

  system("clear");

Example:

 
  system("cal 9 1996 > month.txt");

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