Algunos comandos incorporados se incluyen por razones de eficiencia y existen como comandos externos en primer lugar. Por ejemplo:
$ type -a echo
echo is a shell builtin
echo is /bin/echo
$ type -a printf
printf is a shell builtin
printf is /usr/bin/printf
Se puede encontrar un análisis detallado de los comandos internos y externos en Unix y Linux .
En cuanto a obtener ayuda para comandos internos / externos duales como echo
tiene dos opciones. Un método es mediante el uso de man echo
:
ECHO(1) User Commands ECHO(1)
NAME
echo - display a line of text
SYNOPSIS
echo [SHORT-OPTION]... [STRING]...
echo LONG-OPTION
DESCRIPTION
Echo the STRING(s) to standard output.
-n do not output the trailing newline
-e enable interpretation of backslash escapes
-E disable interpretation of backslash escapes (default)
--help display this help and exit
--version
output version information and exit
If -e is in effect, the following sequences are recognized:
\\ backslash
\a alert (BEL)
Manual page echo(1) line 1 (press h for help or q to quit)
Y puedes escribir:
$ help echo
echo: echo [-neE] [arg ...]
Write arguments to the standard output.
Display the ARGs, separated by a single space character and followed by a
newline, on the standard output.
Options:
-n do not append a newline
-e enable interpretation of the following backslash escapes
-E explicitly suppress interpretation of backslash escapes
`echo' interprets the following backslash-escaped characters:
\a alert (bell)
\b backspace
\c suppress further output
\e escape character
\E escape character
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\0nnn the character whose ASCII code is NNN (octal). NNN can be
0 to 3 octal digits
\xHH the eight-bit character whose value is HH (hexadecimal). HH
can be one or two hex digits
Exit Status:
Returns success unless a write error occurs.