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The echo builtin command

Synopsis

echo [-neE] [arg ...]

Description

echo outputs it's args to stdout, separated by spaces, followed by a newline. The return status is always 0. If the shopt option xpg_echo is set, Bash dynamically determines whether echo should expand escape characters (listed below) by default based on the current platform. echo doesn't interpret -- as the end of options, and will simply print this string if given.

Options

Option Description
-n The trailing newline is suppressed.
-e Interpretation of the following backslash-escaped characters (below) is enabled.
-E Disables the interpretation of these escape characters, even on systems where they are interpreted by default.

Escape sequences

Escape Description
\a alert (bell)
\b backspace
\c suppress further output
\e
\E an escape character
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\0nnn the eight-bit character whose value is the octal value nnn (zero to three octal digits)
\xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
\uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
\UHHHHHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)

Examples

Portability considerations

  • echo is a portability train wreck. No major shell follows POSIX completely, and any shell that attempts to do so should be considered horribly broken. SUSv4 specifies that echo shall not include any options. Further, it specifies that the behavior of -n as a first argument shall be determined by the implementation, unless XSI is followed, in which case -n is always treated as a string, and backslash escapes are interpreted by default. dash has the misfeature of following this and interpreting escapes by default, but includes a -n feature for suppressing newlines nevertheless.

    In practice, if you're able to assume a korn-like shell including bash, mksh, or zsh, echo when used in simple cases is generally reliable. For example, in the very common situation in which echo is supplied with a single argument and whose output is to have a newline appended, using echo is considered common practice.
  • Never use options to echo! Ever! Any time you feel tempted to use echo -e, -n, or any other special feature of echo, use printf instead! If portability is a requirement, you should consider using printf exclusively and just ignore that echo even exists. If you must use echo -e and refuse to use printf, it is usually acceptable to use echo $'…' if targeting only shells that support this special quoting style.
  • ksh93 has a print command, which if coding specifically for ksh93 should be preferred over echo. printf still includes most of the functionality of both, and should usually be the most preferred option.

See also

Discussion

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commands/builtin/echo.txt · Last modified: 2012/05/26 13:14 by ormaaj
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