- echo arguments
The echo utility writes its arguments, separated by BLANKs and terminated by a NEWLINE, to the standard output. If there are no arguments, only the NEWLINE character is written.
echo is useful for producing diagnostics in command files, for sending known data into a pipe, and for displaying the contents of environment variables.
The C shell, the Korn shell, and the Bourne shell all have echo built-in commands, which, by default, is invoked if the user calls echo without a full pathname. See shell_builtins(1). sh's echo, ksh88's echo, ksh's echo, and /usr/bin/echo understand the back-slashed escape characters, except that sh's echo does not understand \a as the alert character. In addition, ksh88's and ksh's echo does not have an -n option. csh's echo and /usr/ucb/echo, on the other hand, have an -n option, but do not understand the back-slashed escape characters. sh and ksh88 determine whether /usr/ucb/echo is found first in the PATH and, if so, they adapt the behavior of the echo builtin to match /usr/ucb/echo.
The following operand is supported:
A string to be written to standard output. If any operand is “-n”, it is treated as a string, not an option. The following character sequences is recognized within any of the arguments:
Print line without new-line. All characters following the \c in the argument are ignored.
Where n is the 8-bit character whose ASCII code is the 1-, 2- or 3-digit octal number representing that character.
Portable applications should not use -n (as the first argument) or escape sequences.
The printf(1) utility can be used portably to emulate any of the traditional behaviors of the echo utility as follows:
The Solaris 2.6 operating environment or compatible version's /usr/bin/echo is equivalent to:
printf "%b\n" "$*"
The /usr/ucb/echo is equivalent to:
if [ "X$1" = "X-n" ] then shift printf "%s" "$*" else printf "%s\n" "$*" fi
New applications are encouraged to use printf instead of echo.
示例 1 Finding how far below root your current directory is located
You can use echo to determine how many subdirectories below the root directory (/) is your current directory, as follows:
Echo your current-working-directory's full pathname.
Pipe the output through tr to translate the path's embedded slash-characters into space-characters.
Pipe that output through wc -w for a count of the names in your path.
example% /usr/bin/echo $PWD | tr '/' ' ' | wc -w
Below are the different flavors for echoing a string without a NEWLINE:
示例 2 /usr/bin/echo
example% /usr/bin/echo "$USER's current directory is $PWD\c"
示例 3 sh/ksh88 shells
example$ echo "$USER's current directory is $PWD\c"
示例 4 csh shell
example% echo -n "$USER's current directory is $PWD"
示例 5 /usr/ucb/echo
example% /usr/ucb/echo -n "$USER's current directory is $PWD"
See environ(5) for descriptions of the following environment variables that affect the execution of uname: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, and NLSPATH.
The following error values are returned:
An error occurred.
See attributes(5) for descriptions of the following attributes:
When representing an 8-bit character by using the escape convention \0n, the n must always be preceded by the digit zero (0).
For example, typing: echo 'WARNING:\ 07' prints the phrase WARNING: and sounds the “bell” on your terminal. The use of single (or double) quotes (or two backslashes) is required to protect the “ \” that precedes the “07”.
Following the \0, up to three digits are used in constructing the octal output character. If, following the \0n, you want to echo additional digits that are not part of the octal representation, you must use the full 3-digit n. For example, if you want to echo “ESC 7” you must use the three digits “033” rather than just the two digits “33” after the \ 0.
2 digits Incorrect: echo "\0337" | od -xc produces: df0a (hex) 337 (ascii) 3 digits Correct: echo "\00337" | od -xc produces: lb37 0a00 (hex) 033 7 (ascii)
For the octal equivalents of each character, see ascii(5).