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93 lines
3.9 KiB
Markdown
93 lines
3.9 KiB
Markdown
# The echo builtin command
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## Synopsis
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echo [-neE] [arg ...]
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## Description
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`echo` outputs it's args to stdout, separated by spaces, followed by a
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newline. The return status is always `0`. If the
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[shopt](../../commands/builtin/shopt.md) option `xpg_echo` is set, Bash
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dynamically determines whether echo should expand escape characters
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(listed below) by default based on the current platform. `echo` doesn't
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interpret `--` as the end of options, and will simply print this string
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if given.
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### Options
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Option Description
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-------- ----------------------------------------------------------------------------------------------------------------
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`-n` The trailing newline is suppressed.
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`-e` Interpretation of the following backslash-escaped characters (below) is enabled.
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`-E` Disables the interpretation of these escape characters, even on systems where they are interpreted by default.
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### Escape sequences
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Escape Description
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-------------- ---------------------------------------------------------------------------------------------------------------
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`\a` alert (bell)
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`\b` backspace
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`\c` suppress further output
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`\e`
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`\E` an escape character
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`\f` form feed
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`\n` new line
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`\r` carriage return
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`\t` horizontal tab
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`\v` vertical tab
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`\\` backslash
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`\0nnn` the eight-bit character whose value is the octal value nnn (zero to three octal digits)
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`\xHH` the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
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`\uHHHH` the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
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`\UHHHHHHHH` the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)
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## Examples
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## Portability considerations
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- `echo` is a portability train wreck. No major shell follows POSIX
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completely, and any shell that attempts to do so should be
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considered horribly broken.
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[SUSv4](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/echo.html#tag_20_37)
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specifies that `echo` **shall not** include any options. Further, it
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specifies that the behavior of `-n` as a first argument shall be
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determined by the implementation, unless XSI is followed, in which
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case `-n` is always treated as a string, and backslash escapes are
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interpreted by default. `dash` has the misfeature of following this
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and interpreting escapes by default, but includes a `-n` feature for
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suppressing newlines nevertheless.\
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\
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In practice, if you\'re able to assume a korn-like shell including
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bash, mksh, or zsh, `echo` when used in simple cases is generally
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reliable. For example, in the very common situation in which echo is
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supplied with a single argument and whose output is to have a
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newline appended, using `echo` is considered common practice.
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```{=html}
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<!-- -->
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```
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- **Never use options to `echo`! *Ever*!** Any time you feel tempted
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to use `echo -e`, `-n`, or any other special feature of echo, **use
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[printf](../../commands/builtin/printf.md) instead!** If portability is a
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requirement, you should consider using `printf` *exclusively* and
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just ignore that `echo` even exists. If you must use `echo -e` and
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refuse to use `printf`, it is usually acceptable to use \'\'echo
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\$\'\...\' \'\'if targeting only shells that support this special
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quoting style.
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```{=html}
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<!-- -->
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```
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- `ksh93` has a `print` command, which if coding specifically for
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`ksh93` should be preferred over `echo`.
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[printf](../../commands/builtin/printf.md) still includes most of the
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functionality of both, and should usually be the most preferred
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option.
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## See also
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- [printf](../../commands/builtin/printf.md)
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- <http://cfajohnson.com/shell/cus-faq.html#Q0b>
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- <http://www.in-ulm.de/~mascheck/various/echo+printf/>
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