Previous Table of Contents Next


Module 106
print (ksh)

DESCRIPTION

The internal print command is a sophisticated echo command. It is the ksh's output command. The print command performs like echo unless options are used to change how it functions. Refer to the echo command described in Module 38.

COMMAND FORMAT

Following is the general format of the print command.

   print [ - ] [ -nprRsu[n] ] [ args Options  The following list describes
   the options and their arguments that may be used to control how print
   functions.
- Ignore all following options. Causes print to perform exactly like the echo (SV) command. Same as no options.
-n Do not write a new-line at the end of the output. Performs the same function as the \c escape sequence. Conforms to BSD echo -n option.
-r Ignore the escape sequences used in the echo command.
-R Same as -r. Also ignores all options except for -n.
-s Write all arguments (the output) to the history file.
-un Write all arguments (the output) to the file with file descriptor n. No new-line is written on the output.
-p Write all arguments (the output) to the pipe process spawned with the |& command.

The following examples will help clarify the use of these options.

   cj> print -R -n "This \n is a prompt:" # ignores the \n and no new-line
   This is a prompt:cj>
   cj> print -s "vi mmrg"                 # enter the "vi mmrg" command
                                          # into the history file
   cj> print -p "Some info on the pipe"   # write to the hidden shell pipe.

Arguments

The arguments to echo are whatever text you wish to write to the standard output. If no arguments are specified, then echo displays a blank line by writing a single new-line. You can use the following list of escape sequence characters to produce special output from echo:


CAUTION:  
You must remember that the shell interprets the \ (backslash) as a special character. Therefore, it is recommended that you place your echo arguments inside double quotes.



\b produces a backspace on the output
\c write the output, but do NOT terminate it with a new-line
\f produces a form feed
\n produces a new-line
\r produces a carriage return
\t produces a tab
\v produces a vertical tab
\\ produces a backslash
\0n produces the ASCII character with the octal code of n. Where n is a 1-, 2-, or 3-digit octal number representing the desired character.

DIAGNOSTICS AND BUGS

When you use the \0n escape sequence you must always precede the n with a 0 (zero). This informs echo that the number is octal.

To use escape sequences you must either enclose them in double quotes, single quotes, or use two \ (backslashes).

If you need to use these escape characters, the octal equivalents can be found in Appendix G.

RELATED COMMANDS

Refer to the echo command described in Module 38 and the ksh command described in Module 71.

RELATED FILES

The output of print is sent to the standard output. Therefore, you may redirect it to a file or a pipe. It is also possible to send the output to the shell's background pipe, using the -p option. Refer to the |& (vertical bar, ampersand) definition in the SPECIAL (META) CHARACTERS section of Module 71 on the ksh.

APPLICATIONS

The print command is used to display text and variables to the user's terminal. Since the standard output is the default, output may be redirected as desired. It is often used to direct known output into a pipe. The pipe may be the shell's own background pipe or a normal pipe. It is used in shell scripts to display return codes and debugging output. You use print to build menus and data entry screens. The select command should also be studied for menu building.

TYPICAL OPERATION

In this activity you use the echo command to display text and variables. You also use it to output new-lines, tabs, and no new-line via escape sequences. If you don't have the ksh, skip to the next module. Begin at the shell prompt.

1.  Type print -R -n "My user name is $LOGNAME" and press Return. Notice your prompt is displayed at the end of the text. The -n informs print not to write a new-line to the output.
2.  Type bc |& and press Return. No response occurs. Make a note of the process ID displayed.
3.  Type print -p "2 * 2" and press Return. Notice the string is not displayed; it is sent to the command in background (step 2).
4.  Type read -r -p ANS and press Return. No response occurs.
5.  Type echo $ANS and press Return. The number 4 is displayed, the result of 2 * 2 which was multiplied by the bc command.
6.  Type kill -9 pid and press Return, where pid is the number of the process you wrote down in step 2.
7.  Type print -s "print this" and press Return. No response occurs.
8.  Press Escape, type k, and press Return. Notice the previously entered "print this" appears on your command line. When you pressed Esc k you entered the vi in-line editor command mode. The k moved you up one line in the history file.
     cj> Escapek ...
     cj> print this        # appeared after you pressed Escapek
     this                  # appeared after you pressed Return
9.  Turn to Module 10 to continue the learning sequence.


Previous Table of Contents Next