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special characters in linux - when is \t a tab or the time
Posted on 2011-03-05
Hi
I'm not sure in linux how the difference between special characters work. When is \t a tab or the time. If i wanted to output a tab i could write
echo $'\t'
but if i wanted to set the shell prompt to show the time i would write
PS1='\t'
Why are they treated differently when both times i am creating a string?
thanks
I'm not sure in linux how the difference between special characters work. When is \t a tab or the time. If i wanted to output a tab i could write
echo $'\t'
but if i wanted to set the shell prompt to show the time i would write
PS1='\t'
Why are they treated differently when both times i am creating a string?
thanks
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3 Comments
This is all about bash(shell) and how it handles the special characters.
You can
echo "\t" # displays \t
echo -e "\t" # displays tab
but PS1='\t' # uses time in prompt
So again, You always have to refer manual/documentation to find how an application handles special or escaped characters.
There's no such thing like \t always means tabulator.
You can
echo "\t" # displays \t
echo -e "\t" # displays tab
but PS1='\t' # uses time in prompt
So again, You always have to refer manual/documentation to find how an application handles special or escaped characters.
There's no such thing like \t always means tabulator.
It depends on the context. There are no "universal" special characters. The C programming language defines a number of special characters that have become sort of defacto standards, primarily because much of the programs involved in the OS are written in either C or C++. But those special characters in C are defined only for character constants in programs and for certain output routines. It doesn't happen automatically in any string.
So, how special characters are handled on input depends on the program getting the input (also on the tty device driver if input is from a terminal). So, in this case the characters "\" and "t" are both actually stored in the string input. In the case of the bash shell, it is assigned to the PS1 variable as is, with no translation. Then, as part of the shell output routine, when it sees the "\t" in the prompt variable, instead of outputing the "\t", it outputs the current time.
So, how special characters are handled on input depends on the program getting the input (also on the tty device driver if input is from a terminal). So, in this case the characters "\" and "t" are both actually stored in the string input. In the case of the bash shell, it is assigned to the PS1 variable as is, with no translation. Then, as part of the shell output routine, when it sees the "\t" in the prompt variable, instead of outputing the "\t", it outputs the current time.
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