echo (command)

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 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.

History

echo began within Multics, and became part of Version 2 Unix. echo -n in Version 7 replaced prompt, which behaved like the command without a newline.[3]

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[4] 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"`.

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. ↑ McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. 139.
  4. ↑ IEEE Std 1003.1, 2004, documentation for echo

External links

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