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89 lines
5.2 KiB
Markdown
89 lines
5.2 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) 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 considered
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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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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 newline
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appended, using `echo` is considered common practice.
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<!-- -->
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- **Never use options to `echo`! *Ever*!** Any time you feel tempted to
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use `echo -e`, `-n`, or any other special feature of echo, **use
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[printf](/commands/builtin/printf) instead!** If portability is a
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requirement, you should consider using `printf` *exclusively* and just
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ignore that `echo` even exists. If you must use `echo -e` and refuse
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to use `printf`, it is usually acceptable to use ''echo \$'...' ''if
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targeting only shells that support this special quoting style.
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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) 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)
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- <http://cfajohnson.com/shell/cus-faq.html#Q0b>
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