What’s the difference between single (') and double (") quotes in Vim? Does it make speed differences? Is it better to use one or another when running functions inside it? Does it matter at all?
I’m interested specifically in their use in the .vimrc file.
I’m asking because I find people use both in the same thing, and I’m wondering what are the differences. I tried to Google this, but wasn’t able to find anything.
Double quotes allow for interpolation whereas single quotes do not.
For example, using double quotes :echo "foo\nbar" will output foo and bar on separate lines whereas :echo 'foo\nbar' will not interpret \n as a line break and will output foo\nbar literally.
For more info on different types of quotes type :h 41.2 for the help file and read the part near the end of the section with the heading STRING VARIABLES AND CONSTANTS.
This said, don't confuse quotes for strings with the double quote at the beginning of a line comment. Single quotes never start line comments, only double quotes do.
Related
I want to run a command from a bash script which has single quotes and some other commands inside the single quotes and a variable.
e.g. repo forall -c '....$variable'
In this format, $ is escaped and the variable is not expanded.
I tried the following variations but they were rejected:
repo forall -c '...."$variable" '
repo forall -c " '....$variable' "
" repo forall -c '....$variable' "
repo forall -c "'" ....$variable "'"
If I substitute the value in place of the variable the command is executed just fine.
Please tell me where am I going wrong.
Inside single quotes everything is preserved literally, without exception.
That means you have to close the quotes, insert something, and then re-enter again.
'before'"$variable"'after'
'before'"'"'after'
'before'\''after'
Word concatenation is simply done by juxtaposition. As you can verify, each of the above lines is a single word to the shell. Quotes (single or double quotes, depending on the situation) don't isolate words. They are only used to disable interpretation of various special characters, like whitespace, $, ;... For a good tutorial on quoting see Mark Reed's answer. Also relevant: Which characters need to be escaped in bash?
Do not concatenate strings interpreted by a shell
You should absolutely avoid building shell commands by concatenating variables. This is a bad idea similar to concatenation of SQL fragments (SQL injection!).
Usually it is possible to have placeholders in the command, and to supply the command together with variables so that the callee can receive them from the invocation arguments list.
For example, the following is very unsafe. DON'T DO THIS
script="echo \"Argument 1 is: $myvar\""
/bin/sh -c "$script"
If the contents of $myvar is untrusted, here is an exploit:
myvar='foo"; echo "you were hacked'
Instead of the above invocation, use positional arguments. The following invocation is better -- it's not exploitable:
script='echo "arg 1 is: $1"'
/bin/sh -c "$script" -- "$myvar"
Note the use of single ticks in the assignment to script, which means that it's taken literally, without variable expansion or any other form of interpretation.
The repo command can't care what kind of quotes it gets. If you need parameter expansion, use double quotes. If that means you wind up having to backslash a lot of stuff, use single quotes for most of it, and then break out of them and go into doubles for the part where you need the expansion to happen.
repo forall -c 'literal stuff goes here; '"stuff with $parameters here"' more literal stuff'
Explanation follows, if you're interested.
When you run a command from the shell, what that command receives as arguments is an array of null-terminated strings. Those strings may contain absolutely any non-null character.
But when the shell is building that array of strings from a command line, it interprets some characters specially; this is designed to make commands easier (indeed, possible) to type. For instance, spaces normally indicate the boundary between strings in the array; for that reason, the individual arguments are sometimes called "words". But an argument may nonetheless have spaces in it; you just need some way to tell the shell that's what you want.
You can use a backslash in front of any character (including space, or another backslash) to tell the shell to treat that character literally. But while you can do something like this:
reply=\”That\'ll\ be\ \$4.96,\ please,\"\ said\ the\ cashier
...it can get tiresome. So the shell offers an alternative: quotation marks. These come in two main varieties.
Double-quotation marks are called "grouping quotes". They prevent wildcards and aliases from being expanded, but mostly they're for including spaces in a word. Other things like parameter and command expansion (the sorts of thing signaled by a $) still happen. And of course if you want a literal double-quote inside double-quotes, you have to backslash it:
reply="\"That'll be \$4.96, please,\" said the cashier"
Single-quotation marks are more draconian. Everything between them is taken completely literally, including backslashes. There is absolutely no way to get a literal single quote inside single quotes.
Fortunately, quotation marks in the shell are not word delimiters; by themselves, they don't terminate a word. You can go in and out of quotes, including between different types of quotes, within the same word to get the desired result:
reply='"That'\''ll be $4.96, please," said the cashier'
So that's easier - a lot fewer backslashes, although the close-single-quote, backslashed-literal-single-quote, open-single-quote sequence takes some getting used to.
Modern shells have added another quoting style not specified by the POSIX standard, in which the leading single quotation mark is prefixed with a dollar sign. Strings so quoted follow similar conventions to string literals in the ANSI standard version of the C programming language, and are therefore sometimes called "ANSI strings" and the $'...' pair "ANSI quotes". Within such strings, the above advice about backslashes being taken literally no longer applies. Instead, they become special again - not only can you include a literal single quotation mark or backslash by prepending a backslash to it, but the shell also expands the ANSI C character escapes (like \n for a newline, \t for tab, and \xHH for the character with hexadecimal code HH). Otherwise, however, they behave as single-quoted strings: no parameter or command substitution takes place:
reply=$'"That\'ll be $4.96, please," said the cashier'
The important thing to note is that the single string that gets stored in the reply variable is exactly the same in all of these examples. Similarly, after the shell is done parsing a command line, there is no way for the command being run to tell exactly how each argument string was actually typed – or even if it was typed, rather than being created programmatically somehow.
Below is what worked for me -
QUOTE="'"
hive -e "alter table TBL_NAME set location $QUOTE$TBL_HDFS_DIR_PATH$QUOTE"
EDIT: (As per the comments in question:)
I've been looking into this since then. I was lucky enough that I had repo laying around. Still it's not clear to me whether you need to enclose your commands between single quotes by force. I looked into the repo syntax and I don't think you need to. You could used double quotes around your command, and then use whatever single and double quotes you need inside provided you escape double ones.
just use printf
instead of
repo forall -c '....$variable'
use printf to replace the variable token with the expanded variable.
For example:
template='.... %s'
repo forall -c $(printf "${template}" "${variable}")
Variables can contain single quotes.
myvar=\'....$variable\'
repo forall -c $myvar
I was wondering why I could never get my awk statement to print from an ssh session so I found this forum. Nothing here helped me directly but if anyone is having an issue similar to below, then give me an up vote. It seems any sort of single or double quotes were just not helping, but then I didn't try everything.
check_var="df -h / | awk 'FNR==2{print $3}'"
getckvar=$(ssh user#host "$check_var")
echo $getckvar
What do you get? A load of nothing.
Fix: escape \$3 in your print function.
Does this work for you?
eval repo forall -c '....$variable'
I have a pattern where there are double-quotes between numbers in a CSV file.
I can search for the pattern by [0-9]\"[0-9], but how do I retain value while removing the double quote. CSV format is like this:
"1234"5678","Text1","Text2"
"987654321","Text3","text4"
"7812891"3","Text5","Text6"
As you may notice there are double quotes between some numbers which I want to remove.
I have tried the following way, which is incorrect:
:%s/[0-9]\"[0-9]/[0-9][0-9]/g
Is it possible to execute a command at every search pattern, maybe go one character forward and delete it. How can "lx" be embedded in search and replace.
You need to capture groups. Try:
:%s/\(\d\)"\(\d\)/\1\2/g
[A digit can also be denoted by \d.]
I know that this question has been answered already, but here's another approach:
:%s/\d\zs"\ze\d
Explanation:
%s Substitute for the whole buffer
\d look up for a digit
\zs set the start of match here
" look up for a double-quote
\ze set the end of match here
\d look up for a digit
That makes the substitute command to match only the double-quote surrounded by digits.
Omitting the replacement string just deletes the match.
You need boundaries to use in regular expression.
Try this:
:%s/\([0-9]\)"\([0-9]\)/\1\2/g
A bit naive solution:
%s/^"/BEGINNING OF LINE QUOTE MARK/g
%s/\",\"/quote comma quote/g
%s/\"$/quota end of line/g
%s/\"//g
%s/quota end of line/"/g
%s/quote comma quote/","/g
%s/BEGINNING OF LINE QUOTE MARK/"/g
A macro can be created quite easy out of it and invoked as many times as needed.
I have the following command
cmd '"asdf" "a'sdf"'
I need to surround the arguments with single quotes only. cmd doesnt work with double quotes for some reason I dont know. The above command doesnt work because the single in the middle terminates the first single quote. If I escape, to the following
cmd '"asdf" "a\'sdf"'
It still doesnt work. How do I get this working?
According to the bash man page:
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.
So the answer is, you can't include a single quote within a single-quoted string no matter how you try. But depending on how your script is set up you may be able to use '\'', which will end the first single quote, escape the second, and start another single-quoted string with the third.
A long long time ago, a mentor suggested I use constructs like '"asdf" "a'"'"'sdf"'. It works, but it's bizarre to look at.
Since you can't put single quotes inside single quotes, escaping them like '"asdf" "a'\''sdf' may be the way to go.
Note that you can also use printf and variables interactively or within a shell script. With most shells (you haven't specified what you're using), you should get the similar results to this:
$ fmt='"asdf" "a%ssdf"\n'
$ printf "$fmt" "'"
"asdf" "a'sdf"
$
or you could even include the single quote using its ASCII value:
$ fmt='"asdf" "a\047sdf"\n'
$ printf "$fmt"
"asdf" "a'sdf"
$
or in csh:
% set fmt='"asdf" "a\047sdf"\n'
% printf "$fmt"
"asdf" "a'sdf"
%
This is shell-independent because if your shell doesn't have a printf command built in (as Bash has), then the command will most likely exist as a separate binary in /bin or /usr/bin.
I don't know your use case, so it's difficult to come up with a solution that I know will be applicable.
Well, you can always use autocomplete to help you find the answer.
For instance, if I have a file with an apostrophe in it, but I want to surround the path with single quotes, I can do this (using cat as an example command where the file is named sam's file.txt):
cat 'sam[press tab here]
and it autocompletes to this, for me:
cat 'sam'\''s\ file.txt
So, apparently it is possible. Another answerer mentioned the '\'' thing first, but I figured I'd tell you one way to try to figure it out if that's not working for you (and I thought I'd be another witness to tell you the other answer seems to work).
I am looking for some best practices as far as handling csv and tab delimited files.
For CSV files I am already doing some formatting if a value contains a comma or double quote but what if the value contains a new line character? Should I leave the new line intact and encase the value in double quotes + escape any double quotes within the value?
Same question for tab delimited files. I assume the answer would be very similar if not the same.
Usually you keep \n unaltered while exploiting the fact that the newline char will be enclosed in a " " string. This doesn't create ambiguities but it's really ugly if you have to take a look to the file using a normal texteditor.
But it is how you should do since you don't escape anything inside a string in a CSV except for the double quote itself.
#Jack is right, that your best bet is to keep the \n unaltered, since you'll expect it inside of double-quotes if that is the case.
As with most things, I think consistency here is key. As far as I know, your values only need to be double-quoted if they span multiple lines, contain commas, or contain double-quotes. In some implementations I've seen, all values are escaped and double-quoted, since it makes the parsing algorithm simpler (there's never a question of escaping and double-quoting, and the reverse on reading the CSV).
This isn't the most space-optimized solution, but makes reading and writing the file a trivial affair, for both your own library and others that may consume it in the future.
For TSV, if you want lossless representation of values, the "Linear TSV" specification is worth considering: http://paulfitz.github.io/dataprotocols/linear-tsv/index.html
For obvious reasons, most such conventions adhere to the following at a minimum:
\n for newline,
\t for tab,
\r for carriage return,
\\ for backslash
Some tools add \0 for NUL.
I have something akin to <Foobar Name='Hello There'/> and need to change the single quotation marks to double quotation marks. I tried :s/\'.*\'/\"\0\" but it ended up producing <Foobar Name="'Hello There'"/>. Replacing the \0 with \1 only produced a blank string inside the double quotes - is there some special syntax I'm missing that I need to make only the found string ("Hello There") inside the quotation marks assign to \1?
There's also surround.vim, if you're looking to do this fairly often. You'd use cs'" to change surrounding quotes.
You need to use groupings:
:s/\'\(.*\)\'/\"\1\"
This way argument 1 (ie, \1) will correspond to whatever is delimited by \( and \).
%s/'\([^']*\)'/"\1"/g
You will want to use [^']* instead of .* otherwise
'apples' are 'red' would get converted to "apples' are 'red"
unless i'm missing something, wouldn't s/\'/"/g work?
Just an FYI - to replace all double quotes with single, this is the correct regexp - based on rayd09's example above
:%s/"\([^"]*\)"/'\1'/g
You need to put round brackets around the part of the expression you wish to capture.
s/\'\(.*\)\'/"\1"/
But, you might have problems with unintentional matching. Might you be able to simply replace any single quotes with double quotes in your file?
You've got the right idea -- you want to have "\1" as your replace clause, but you need to put the "Hello There" part in capture group 1 first (0 is the entire match). Try:
:%/'\(.*\)'/"\1"
Shift + V to enter visual block mode. Highlight the lines of code you want to remove single quotes from.
Then hit : on keyboard
Then type
s/'//g
Press Enter.
Done. You win.
Presuming you want to do this on an entire file ...
N Mode:
ggvG$ [SHIFT+:]
X Mode:
'<,'>/'/" [RET]