Echo and Printf! Difference between them in displaying Output, Part 1 - AkuCode
Echo, and why should you avoid it?
When I started writing
shell scripts, I immediately learned about two branches of Unix: AT & T
system V and BSD. One of their differences is the result of ECHO. Created in
all the modern bash shell, echo prints its arguments with one space between
them into a standard output stream, followed by a new line:
Echo Quick Brown fox
The Quick Brown Fox
A new by default can
be pressed into one of the events, depending on the shell;
echo -n No newline
No newline$ echo “No newline\c”
No newline$
The BSD variation of the
The echo accepts the-e option, which presses a new line. The AT & T version
uses an escape sequence, c, to do the same thing. Or vice versa? I'm having
trouble remembering which is because even though I use the AT & T
system (Hardware and operating system), the Echo command received both the AT
& T and BSD syntax.
Of course, it is a history
on the Bash shell Learning, we are dealing with bash. Bash has the-e option to
enable escape sequences such as c but by default the-N usage to prevent new
rows from being printed. (The escape sequence identified by "echo"-e
is the same as that described in the next section with the addition of c).
The problem is that bash
has the option xpg_echo (XPG stands for the X/Open portability Guide, the
specifications for the Unix system) which makes the echo behave like any other
version. And it can be turned on and off while it is in the bash shell (using
shopt-s xpg_echo either in the command line or inside the script), or it can be
activated when the shell is compiled. In other words even in bash, you can't
really be sure what results you'll get.
If you restrict the use
of echo for a current situation where there could not be a conflict, that is
when you are sure the argument does not start with-N and does not contain
escape sequences, you will be safe enough. For others or if you're unsure, use
printf.
Printf: Format and print data
Derived from the C
programming language function with the same name, the Shell printf command has
the same purpose but differs in some detail. Like the C function, it uses a
string format to show how it presents its arguments:
Printf FORMAT ARG
The FORMAT String can
contain regular characters, breakout sequences, and formatting specifiers. The
usual characters they represent. The format picker is replaced with an argument
from the command line.
Escape Sequences
Is a single letter
preceded by a backslash:
· \a:
Alert (bell)
· \b:
backspace
· \e:
escape character
· \f:
form feed
· \n:
newline
· \r:
carriage return
· \t:
horizontal tab
· \v:
vertical tab
· \\:
backslash
· \nnn:
Characters defined by one to three octal digits
· \xHH:
Characters specified by one to two digits DataReader
The backslash must be protected from the shell with quotation marks or other Backslash:
Printf “Q\t\141\n\x42\n”
Q a
B
Articles that learn about printf are still ongoing and will be available in the next post!
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