echo (command)

Source: Wikipedia, the free encyclopedia.
echo
TypeCommand

In

arguments. It is a command available in various operating system shells and typically used in shell scripts and batch files to output status text to the screen[1] or a computer file, or as a source part of a pipeline
.

Implementations

The command is available in the following operating systems:

Many shells, including all

zsh[15]) and Csh-like shells as well as COMMAND.COM and cmd.exe implement echo as a builtin command
.

The command is also available in the

History

echo began within

Version 2 Unix. echo -n in Version 7 replaced prompt, (which behaved like echo but without terminating its output with a line delimiter).[17]

On

Unix System III, echo started expanding C escape sequences such as \n with the notable difference that octal escape sequences were expressed as \0ooo instead of \ooo in C.[18]

zsh
and GNU echo.

On MS-DOS, the command is available in versions 2 and later.[20]

Nowadays, several incompatible implementations of echo exist on different operating systems (often several on the same system), some of them expanding escape sequences by default, some of them not, some of them accepting options (the list of which varying with implementations), some of them not.

The POSIX specification of echo[21] leaves the behaviour unspecified if the first argument is -n or any argument contain backslash characters while the Unix specification (XSI option in POSIX) mandates the expansion of (some) sequences and does not allow any option processing. In practice, many echo implementations are not compliant in the default environment.

Because of these variations in behaviour, echo is considered a non-portable command on Unix-like systems[22] and the printf command (where available, introduced by Ninth Edition Unix) is preferred instead.

Usage examples

C:\>echo Hello world
Hello world

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

Using a UNIX System III-style implementation:

BGRED=`echo "\033[41m"`
FGBLUE=`echo "\033[35m"`
BGGREEN=`echo "\033[42m"`

NORMAL=`echo "\033[m"`

Or a Unix Version 8-style implementation (such as Bash when not in Unix-conformance mode):

BGRED=`echo -e "\033[41m"`
FGBLUE=`echo -e "\033[35m"`
BGGREEN=`echo -e "\033[42m"`

NORMAL=`echo -e "\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}"

Portably with printf:

BGRED=`printf '\33[41m'`
NORMAL=`printf '\33[m'`
printf '%s\n' "${BGRED}Text on red background${NORMAL}"

See also

References

  1. – via Internet Archive.
  2. ^ "Multics Commands". www.multicians.org.
  3. ^ "FLEX 9.0 User's Manual" (PDF).
  4. ^ "Manual" (PDF). www.pagetable.com. Retrieved 2020-09-12.
  5. ^ "Z80-RIO OPERATING SYSTEM USER'S MANUAL" (PDF).
  6. .
  7. ^ "Chris's Acorns: Panos". chrisacorns.computinghistory.org.uk.
  8. ^ "FlexOS™ User's Guide" (PDF). Archived from the original (PDF) on 2018-09-14.
  9. ^ "OS/2 Batch File Commands". Archived from the original on 2019-04-14.
  10. ^ "echo". docs.microsoft.com. 2 October 2023.
  11. ^ "reactos/reactos". GitHub. 3 January 2022.
  12. ^ "MPE/iX Command Reference Manual" (PDF). Archived from the original (PDF) on 2018-10-21. Retrieved 2018-10-21.
  13. ^ "Shell - KolibriOS wiki". wiki.kolibrios.org.
  14. ^ "Bash Builtins (Bash Reference Manual)". www.gnu.org.
  15. ^ "zsh: 17 Shell Builtin Commands". zsh.sourceforge.net.
  16. ^ "EFI Shells and Scripting". Intel. Retrieved 2013-09-25.
  17. (PDF) (Technical report). CSTR. Bell Labs. 139.
  18. ^ Mascheck, Sven. "echo and printf behaviour". Retrieved 24 July 2016.
  19. ^ "8th Edition Unix echo man page". Retrieved 24 July 2016.
  20. .
  21. ^ "Autoconf documentation on echo portability". Free Software Foundation. Retrieved 24 July 2016.

Further reading

External links