3.5 KiB
====== 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 =====
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''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.
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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.
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''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 =====