Use "${(@f)$(somecommand)}" to get an array of lines from the command's output. Please note that with most of the previous examples, one could have simply left off the subshell and do a simple compare directly with for example the variable, i.e. I need to run the following statement to get the output of foo and store it in a variable while The old advice used to be to double-quote any expression involving a $VARIABLE, at least if one wanted it to be interpreted by the shell as one single item, otherwise, any spaces in the content of $VARIABLE would throw off the shell. UNIX is a registered trademark of The Open Group. Command substitution undergoes field splitting if unquoted: echo $(echo 'a'; echo '*') prints a * (with a single space) whereas echo "$(echo 'a'; echo '*')" prints the unmodified two-line string. This is almost never desirable, hence the general principle to always use double quotes around variable substitutions (unless you know that you need pathname expansion or field splitting): echo "$myvar". Which satellite provided the data? In bash I need to use some equivalent of double quotes inside double quotes (or the other way around.) It's not in the environment until you export it: puts a variable named "MY_HOME" in almost all shells (csh, tcsh excepted). After this assignment, you can use the value of thevariable, e.g. POSIX prohibits that behaviour in non-interactive shells, but a few shells including bash (except in POSIX mode) and ksh88 (including when found as the (supposedly) POSIX sh of some commercial Unices like Solaris) still do it there (bash does also attempt splitting and the redirection fails unless that split+globbing results in exactly one word), which is why it's better to quote targets of redirections in a sh script in case you want to convert it to a bash script some day, or run it on a system where sh is non-compliant on that point, or it may be sourced from interactive shells. Where did all the old discussions on Google Groups actually come from? Some very old shells required export to be used each time you changed a variable name, but all modern shells keep track of assignments for environment variables, so that the following snippet echoes bar: Also, some very old shells required separate commands for myvar=foo and export myvar, but all modern shells understand export myvar=foo. What sort of work environment would require both an electronic engineer and an anthropologist? (max 2 MiB). Tikz getting jagged line when plotting polar function. To get the value held in a variable, you have to provide the dollar sign $. How to deal with filenames containing a single quote inside a zsh completion function? * Variable - Yes * * First, we’ll assign the variable: test="This is a test" The reason why shell variables don't automatically become environment variables is partly that a script might accidentally use a variable name that's meaningful to a program that it launches, and partly just historical. This is important for accurate passing of information. Keeping $ as a special character within double quotes permits referencing a quoted variable ("$variable"), that is, replacing the variable with its value (see Example 4-1, above). In the case of a simple assignment, othervar=$myvar in fact reliably copies the value of myvar to othervar, because globbing and word splitting are inhibited in assignments (because they create multiple words, but a single word is expected). It only takes a minute to sign up. It would be nice to see a summary of when double-quoting is necessary. See, Also, for anyone who is interested, the formal names of. Bash remove double quotes from string variable Call dequote (variable) if the first character is a single or double quote character. MY_HOME="/home/my_user" sets the shell variable called MY_HOME. The same goes for command substitution: "$(foo)" is a command substitution, $(foo) is a command substitution followed by split+glob. They have no effect. I defined some environment variables in my .profile like this: but the variable does not seem to evaluate unless I strip off the quotes and re-source the file. I think you're confused about terminology. MY_HOME="/home/my_user" sets the shell variable called MY_HOME. Double-quotes group substrings, but allows whatever shell you use to do variable substitution. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. It seems like if we have more than 1 empty space in a variable and if those spaces are important we need wrap our variable in quotes! First, separate zsh from the rest. Linux is a registered trademark of Linus Torvalds. Bash For Loop iterates specific set of statements over words in a string, lines in a string or elements in a sequence with the help of examples. Word splitting doesn't happen in a case pattern, but an unquoted variable is interpreted as a pattern whereas a quoted variable is interpreted as a literal string. In fact, you need to leave the quotes out in order for a variable to be parsed as an arithmetic expression. Updated on October 2nd, 2018 in #linux Here's Why You Should Quote Your Variables in Bash Technically you don't have to place quotes around your variables but if you ignore doing it, you may encounter unexpected And of course if you want a literal double-quote inside double-quotes, you have to backslash it: echo "\"That'll be \$4.96, please,\" said the cashier". Single-quotation marks are more draconian. Thanks so very much Rem -----start @echo off cls for /f %%i in (c:\temp\installs.txt) do What every program knows about and transmits to its children is environment variables. For example, if the variable contains path to file, and the filename contains spaces anywhere in the path, the command you are trying to run may fail or give inaccurate results. with echo "$MY_HOME". You do need double quotes as usual within single brackets [ … ] because they are ordinary shell syntax (it's a command that happens to be called [). So if you want to remember a simple rule, just always use double quotes around variable substitutions. Note that you do need double quotes in a case pattern. Rule of thumb: If your variable contains more than 1 consecutive white space and that white space is important for any reason then you DEFINITELY want to wrap your variable in quotes. If there are special characters, you need to protect them with single quotes or double quotes or backslashes or a combination thereof. Here are all the cases I can think of in a Bourne-style shell where you can write a variable or command substitution without double quotes, and the value is interpreted literally. Shell variables are an internal shell concept. Concatenate files placing an empty line between them. Is the identity map the only map from the positive integers to itself that simultaneously preserves multiplication, order, and primes? When that shell instance terminates, MY_HOME is forgotten. The difference between single and double quotes becomes more important when you’re dealing with variables on the command line—by default, bash is going to expand a variable like $test into the full string. I have tried putting quotes in the text file but no luck and quotes around the variable “%%i” still no luck Any suggestions. Hello I have a tiny bit of a problem. What every program knows about and transmits to its children is environment variables. Since your example assignment does not have any variables in it, the double-quotes could have appeared as single-quotes. The @ parameter expansion flag sometimes requires double quotes around the whole substitution: "${(@)foo}". Shell variables are an internal shell concept. How to iterate over list of files the right way? Except that you do need double quotes where a pattern or regular expression is expected: on the right-hand side of = or == or != or =~. Why do options in a quoted variable fail, but work when unquoted? The shell expands the results of variable substitutions $foo further, performing field (word) splitting and pathname expansion (globbing). If the value you're assigning to the variable doesn't contain any characters that are special to the shell, you don't need any quotes. Use "$(somecommand)" to get the output of the command in a single word, sans final newlines. Shells are programming languages, and have variables (also called parameters). How do I run more than 2 circuits in conduit? I have looked around and are just getting more confused. Therefore, based on this experiment, it seems that, in bash, one can omit the double quotes inside [[ ... ]], but not inside [ ... ] nor in command-line arguments, whereas, in zsh, the double quotes may be omitted in all these cases. Here is how to have both the single quotes and the actual value of the variable expanded. Do GFCI outlets require more than standard box volume? What situations exist where Bash variables should not be double quoted? Conversely, a shell variable that is defined in a shell script will become an environment variable if you export it. How to prevent players from having a specific item in their inventory? In a redirection in non-interactive POSIX shells (not bash, nor ksh88). Use double quotes to … By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy, 2021 Stack Exchange, Inc. user contributions under cc by-sa, https://unix.stackexchange.com/questions/16303/what-is-the-significance-of-single-and-double-quotes-in-environment-variables/16306#16306, https://unix.stackexchange.com/questions/16303/what-is-the-significance-of-single-and-double-quotes-in-environment-variables/16305#16305, Can you please explain "Quoting is mostly orthogonal." I've changed “where” to “when” and reinforced the sentence as you suggested. Making statements based on opinion; back them up with references or personal experience. $var never expands to multiple words, however it expands to the empty list (as opposed to a list containing a single, empty word) if the value of var is the empty string. Unix & Linux Stack Exchange works best with JavaScript enabled, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company, Learn more about hiring developers or posting ads with us, Your observed behaviour in zsh depends on the settings and is influenced by the, As an aside -- all-caps variable names are used by variables with meaning to the operating system and shell; the POSIX specification explicitly advises using lower-case names for application defined variables. Variables in quotation marks " are treated as variables. For instance, in bash: In zsh, on the other hand, the same three commands succeed. Nothing is in the environment until you export it. We all know that inside single quotes, all special characters are ignored by the shell, so you can use double quotes inside it. Great graduate courses that went online recently. 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