Echo (command)

From Wikipedia, the free encyclopedia

In computing, echo is a command in DOS, OS/2, Microsoft Windows, Singularity, Unix and Unix-like operating systems that places a string on the computer terminal. It is a built-in command typically used in shell scripts and batch files to output status text to the screen or a file.

Many shells, including Bash[1] and zsh,[2] implement echo as a builtin command.

Usage example

> echo Hello world
Hello world

Using ANSI escape code SGR sequences, compatible terminals can print out colored text:

FGRED=`echo "\033[31m"`
FGCYAN=`echo "\033[36m"`
BGRED=`echo "\033[41m"`
FGBLUE=`echo "\033[35m"`
BGGREEN=`echo "\033[42m"`
 
NORMAL=`echo "\033[m"`

and after :

echo "${FGBLUE} Text in blue ${NORMAL}"
echo "Text normal"
echo "${BGRED} Background in red"
echo "${BGGREEN} Background in Green and back to Normal ${NORMAL}"

Some variants of Unix, such as Linux, support the options -n and -e, and do not process escape sequences unless the -e option is supplied. For example, FGRED=`echo -e "\033[31m"` might be used under Linux. Unfortunately, such options are non standard[3] due to historical incompatibilities between BSD and System V; the printf command can be used in situations where this is a problem. It is therefore recommended that printf be used to ensure that escape sequences are processed. The equivalent code using printf is simply FGRED=`printf "\033[31m"`.

Implementation example

The echo command can be implemented in the C programming language with only a few lines of code:

#include <stdlib.h>
#include <stdio.h>
/* echo command-line arguments; 1st version */
int main(int argc, char *argv[])
{
  int i;
  for (i = 1; i < argc-1; i++)
  {
    (void) printf("%s%s", argv[i], " ");
  }
  (void) printf("%s%s", argv[argc-1], "\n");
  return EXIT_SUCCESS;
}

Scripting Languages can also emulate echo quite simply:

$ perl -e 'print join " ", @ARGV; print "\n"' This is a test.
This is a test.
$ python -c "import sys; print ' '.join(sys.argv[1:])" This is a test.
This is a test.

See also

References

  1. ↑ https://www.gnu.org/software/bash/manual/html_node/Bash-Builtins.html
  2. ↑ http://zsh.sourceforge.net/Doc/Release/Shell-Builtin-Commands.html
  3. ↑ IEEE Std 1003.1, 2004, documentation for echo

External links

File system
Processes
User environment
Text processing
Shell builtins
Networking
Searching
Documentation
Miscellaneous
Windows command-line programs and built-ins
File system navigation
File management
Disk management
Processes
Registry
User environment
File contents
Shell programming
Networking
Searching
Boot management
Miscellaneous
This article is issued from Wikipedia. The text is available under the Creative Commons Attribution/Share Alike; additional terms may apply for the media files.