I'm trying to set up a program and came across this line in a bash script. Could someone tell me what it does? I'm not very experienced with bash.
export PS1='\e[0;33mmyProject \e[0;32m\[\e]0;\u#\h: \w\a\]${debian_chroot:+($debian_chroot)}\u#\h:\w\$\e[0m '
Thank you very much!
This command does two things. It sets the title of the terminal window, and
sets the bash prompt.
export PS1='\e[0;33mmyProject \e[0;32m\[\e]0;\u#\h: \w\a\]${debian_chroot:+($debian_chroot)}\u#\h:\w\$\e[0m '
Piece by piece:
export PS1=
This sets the PS1 variable, which is contains the bash prompt.
\e[0;33m
\e is translated to the ESC character (ascii=0x1B), which is a Control Sequence Introducer, which signifies the beginning of an ANSI Escape Code. The m character at the end of the sequence indicates that the everything between [ and m is to be interpreted as a ;-separated list of SGR (Select Graphic Rendition) parameters (See here for more information). The 0 clears all previous text formatting, and the 33 sets the text color to yellow.
myProject
This just adds the string myProject to the bash prompt.
\e[0;32m
This clears all the previous text formatting (0) and sets the text color to green. (32)
\[ ... \]
\[ begins a sequence of non-printing characters which ends with \]. Everything between those two delimiters will not be visible in the prompt.
\e]0;\u#\h: \w\a
This sets the title of the terminal window to something like
username#hostname: /current/working/directory
The next bit:
${debian_chroot:+($debian_chroot)}
If the variable $debian_chroot has been defined, then this expression will evaluate to the value of $debian_chroot.
$debian_chroot is a variable that is set in /etc/bash.bashrc. This post explains it a lot better than I can.
\u#\h:\w\$\e[0m
\u evaluates to the username of the current user, \h evaluates to the name of the computer, and \w evaluates to the current working directory. \$ is just the character $. It needs to be escaped because in bash script, the character $ signifies that the following characters are the name of a variable. \e[0m reverts the text formatting back to default.
An image of what the prompt might look like in a terminal:
This is quite a complicated command you have here!
Let's break it down section by section.
export
This means that we are setting a variable to be used in other programs.
PS1=
The name of the variable is PS1.
\e
This is an escaped character. In bash (and most programming languages), Everything with a backslash before it is an escaped character. It is used for when you need to include a control character like a space, or the control key itself in a string. When it's escaped, bash treats it like it's part of the string, and not another control character.
[
This is the start of an array. It's very similar to an array in a C program.
;
This is an end character, it can mean several different things. Here, it's being used to define part of the array.
There is some other stuff here, but it's mostly just data in the array.
:
This is a NOT operand. It is used to determine the inverse of something.
${debian_chroot:+($debian_chroot)}
This is a variable. In bash, variables start with a $.
It is using the variable debian_chroot and adding it to itself if it's not null.
This command is just defining a variable, in this case an array containing information probably about a chroot with a debian install in it.
I want to echo a text like this:
"I'm going to bed at "$'\cc3'"$var"$'\cc'
Sometimes it happens that the $var variable begins with a number and Bash is simply concatenating it or whatever. How could I escape the $var so it is separated but without a space between them?
The ANSI-C Quoting mechanism in Bash uses \cx to generate Control-X. Your use of $'\cc3' generates a Control-C (aka \003 or \x03) character followed by a digit 3.
Superficially, then, you want:
var=01:15
echo "I'm going to bed at "$'\cc'"$var"$'\cc'
which surrounds the time with Control-C characters (though quite why you want that, I'm not clear). If you're after a Unicode character U+0CC3 (KANNADA VOWEL SIGN VOCALIC R — ೃ — if you've got good Unicode support), then you need Bash 4.x and $'\ucc3'.
If you're after something else, you need to explain what you're trying to echo with the ANSI-C Quoting.
You could try sending the control-c using the \nnn format instead of \c:
echo $'I\'m going to bed at \003'"$var"$'\003'
(I changed the quoting slightly just to reduce the the number of context switches used to build the string.)
Or, save the control-c character in a variable:
cc=$'\cc'
echo "I'm going to bed at $cc$var$cc"
I'm writing a Ruby command line application in which the user has to enter a "format string" (much like Date.strptime/strftime's strings).
I tried taking them in as arguments to the command, eg
> torque "%A\n%d\n%i, %u"
but it seems that bash actually removes all backslashes from input before it can be processed (plus a lot of trouble with spaces). I also tried the highline gem, which has some more advanced input options, but that automatically escapes backslashes "\" -> "\\" and provides no alternate options.
My current solution is to do a find-and-replace: "\\n" -> "\n". This would take care of the problem, but it also seems hacky and awful.
I could have users write the string in a text file (complicated for the user) or treat some other character, like "&&", as a newline (still complicated for the user).
What is the best way for users to input escaped characters on the command line?
(UPDATE: I checked the documentation for strptime/strftime, and the format strings for those functions replace newline characters with "%n", tabs with "%t", etc. So for now I'm doing that, but any other suggestions are welcome)
What you're looking for is using single quotes instead of double quotes.
Thus:
> torque '%A\n%d\n%i, %u'
Any string quoted in single quotes 'eg.' is does not go through any expansions and is used as is.
More details can be found in the Quoting section of man bash.
From man bash:
Enclosing characters in single quotes preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash.
p eval("\"#{gets.chomp}\"")
Example use:
\n\b # Input by the user from the keyboard
"\n\b" # Value from the script
%A\n%d\n%i, %u # Input by the user from the keyboard
"%A\n%d\n%i, %u" # Value from the script
In Unix I could run myscript '"test"' and I would get "test".
In Windows cmd I get 'test'.
How can I pass double-quotes as a parameter? I would like to know how to do this manually from a cmd window so I don't have to write a program to test my program.
Another way to escape quotes (though probably not preferable), which I've found used in certain places is to use multiple double-quotes. For the purpose of making other people's code legible, I'll explain.
Here's a set of basic rules:
When not wrapped in double-quoted groups, spaces separate parameters:program param1 param2 param 3 will pass four parameters to program.exe: param1, param2, param, and 3.
A double-quoted group ignores spaces as value separators when passing parameters to programs:program one two "three and more" will pass three parameters to program.exe: one, two, and three and more.
Now to explain some of the confusion:
Double-quoted groups that appear directly adjacent to text not wrapped with double-quotes join into one parameter:hello"to the entire"world acts as one parameter: helloto the entireworld.
Note: The previous rule does NOT imply that two double-quoted groups can appear directly adjacent to one another.
Any double-quote directly following a closing quote is treated as (or as part of) plain unwrapped text that is adjacent to the double-quoted group, but only one double-quote:"Tim says, ""Hi!""" will act as one parameter: Tim says, "Hi!"
Thus there are three different types of double-quotes: quotes that open, quotes that close, and quotes that act as plain-text.
Here's the breakdown of that last confusing line:
" open double-quote group
T inside ""s
i inside ""s
m inside ""s
inside ""s - space doesn't separate
s inside ""s
a inside ""s
y inside ""s
s inside ""s
, inside ""s
inside ""s - space doesn't separate
" close double-quoted group
" quote directly follows closer - acts as plain unwrapped text: "
H outside ""s - gets joined to previous adjacent group
i outside ""s - ...
! outside ""s - ...
" open double-quote group
" close double-quote group
" quote directly follows closer - acts as plain unwrapped text: "
Thus, the text effectively joins four groups of characters (one with nothing, however):
Tim says, is the first, wrapped to escape the spaces
"Hi! is the second, not wrapped (there are no spaces)
is the third, a double-quote group wrapping nothing
" is the fourth, the unwrapped close quote.
As you can see, the double-quote group wrapping nothing is still necessary since, without it, the following double-quote would open up a double-quoted group instead of acting as plain-text.
From this, it should be recognizable that therefore, inside and outside quotes, three double-quotes act as a plain-text unescaped double-quote:
"Tim said to him, """What's been happening lately?""""
will print Tim said to him, "What's been happening lately?" as expected. Therefore, three quotes can always be reliably used as an escape.However, in understanding it, you may note that the four quotes at the end can be reduced to a mere two since it technically is adding another unnecessary empty double-quoted group.
Here are a few examples to close it off:
program a b REM sends (a) and (b)
program """a""" REM sends ("a")
program """a b""" REM sends ("a) and (b")
program """"Hello,""" Mike said." REM sends ("Hello," Mike said.)
program ""a""b""c""d"" REM sends (abcd) since the "" groups wrap nothing
program "hello to """quotes"" REM sends (hello to "quotes")
program """"hello world"" REM sends ("hello world")
program """hello" world"" REM sends ("hello world")
program """hello "world"" REM sends ("hello) and (world")
program "hello ""world""" REM sends (hello "world")
program "hello """world"" REM sends (hello "world")
Final note: I did not read any of this from any tutorial - I came up with all of it by experimenting. Therefore, my explanation may not be true internally. Nonetheless all the examples above evaluate as given, thus validating (but not proving) my theory.
I tested this on Windows 7, 64bit using only *.exe calls with parameter passing (not *.bat, but I would suppose it works the same).
I cannot quickly reproduce the symptoms: if I try myscript '"test"' with a batch file myscript.bat containing just #echo.%1 or even #echo.%~1, I get all quotes: '"test"'
Perhaps you can try the escape character ^ like this: myscript '^"test^"'?
Try this:
myscript """test"""
"" escape to a single " in the parameter.
The 2nd document quoted by Peter Mortensen in his comment on the answer of Codesmith made things much clearer for me. That document was written by windowsinspired.com. The link repeated: A Better Way To Understand Quoting and Escaping of Windows Command Line Arguments.
Some further trial and error leads to the following guideline:
Escape every double quote " with a caret ^. If you want other characters with special meaning to the Windows command shell (e.g., <, >, |, &) to be interpreted as regular characters instead, then escape them with a caret, too.
If you want your program foo to receive the command line text "a\"b c" > d and redirect its output to file out.txt, then start your program as follows from the Windows command shell:
foo ^"a\^"b c^" ^> d > out.txt
If foo interprets \" as a literal double quote and expects unescaped double quotes to delimit arguments that include whitespace, then foo interprets the command as specifying one argument a"b c, one argument >, and one argument d.
If instead foo interprets a doubled double quote "" as a literal double quote, then start your program as
foo ^"a^"^"b c^" ^> d > out.txt
The key insight from the quoted document is that, to the Windows command shell, an unescaped double quote triggers switching between two possible states.
Some further trial and error implies that in the initial state, redirection (to a file or pipe) is recognized and a caret ^ escapes a double quote and the caret is removed from the input. In the other state, redirection is not recognized and a caret does not escape a double quote and isn't removed. Let's refer to these states as 'outside' and 'inside', respectively.
If you want to redirect the output of your command, then the command shell must be in the outside state when it reaches the redirection, so there must be an even number of unescaped (by caret) double quotes preceding the redirection. foo "a\"b " > out.txt won't work -- the command shell passes the entire "a\"b " > out.txt to foo as its combined command line arguments, instead of passing only "a\"b " and redirecting the output to out.txt.
foo "a\^"b " > out.txt won't work, either, because the caret ^ is encountered in the inside state where it is an ordinary character and not an escape character, so "a\^"b " > out.txt gets passed to foo.
The only way that (hopefully) always works is to keep the command shell always in the outside state, because then redirection works.
If you don't need redirection (or other characters with special meaning to the command shell), then you can do without the carets. If foo interprets \" as a literal double quote, then you can call it as
foo "a\"b c"
Then foo receives "a\"b c" as its combined arguments text and can interpret it as a single argument equal to a"b c.
Now -- finally -- to the original question. myscript '"test"' called from the Windows command shell passes '"test"' to myscript. Apparently myscript interprets the single and double quotes as argument delimiters and removes them. You need to figure out what myscript accepts as a literal double quote and then specify that in your command, using ^ to escape any characters that have special meaning to the Windows command shell. Given that myscript is also available on Unix, perhaps \" does the trick. Try
myscript \^"test\^"
or, if you don't need redirection,
myscript \"test\"
I'm calling powershell from cmd, and passing quotes and neither escapes here worked. The grave accent worked to escape double quotes on this Win 10 surface pro.
>powershell.exe "echo la`"" >> test
>type test
la"
Below are outputs I got for other characters to escape a double quote:
la\
la^
la
la~
Using another quote to escape a quote resulted in no quotes.
As you can see, the characters themselves got typed, but didn't escape the double quotes.
Maybe you came here, because you wonder how to escape quotes that you need in the command that you pass to /c on cmd.exe? Well you don't:
CMD /c "MKDIR "foo bar""
will execute
MKDIR "foo bar"
which is really a behavior that I did not expect in the first glance.
I have written a c program that retrieves arguments from the command line under Windows. One of the arguments is a regular expression. So I need to retrieve special characters such as "( , .", etc., but cmd.exe treats "(" as a special character.
How could I input these special character?
thanks.
You can put the arguments in quotes:
myprogram.exe "(this is some text, with special characters.)"
Though I wouldn't assume that parentheses cause problems unless you are using blocks for conditional statements or loops in a batch file. The usual array of characters that are treated specially by the shell and need quoting or escaping are:
& | > < ^
If you use those in your regular expression, then you need quotes, or escape those characters:
myprogram "(.*)|[a-f]+"
myprogram (.*)^|[a-f]+
(^ is the escape character which causes the following character to be not interpreted by the shell but instead used literally)
You can generally prefix any character with ^ to turn off its special nature. For example:
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
C:\Documents and Settings\Pax>echo No ^<redirection^> here and can also do ^
More? multi-line, ^(parentheses^) and ^^ itself
No <redirection> here and can also do multi-line, (parentheses) and ^ itself
C:\Documents and Settings\Pax>
That's a caret followed by an ENTER after the word do.