This goes for both the plain myvar=value syntax and the export utility. @DKBose It means that environment vs shell variables on the one hand, and quoting on the other hand, are two separate issues that have little to do with each other. I've changed “where” to “when” and reinforced the sentence as you suggested. rev 2021.1.11.38289, The best answers are voted up and rise to the top. What situations exist where Bash variables should not be double quoted? Inside the shell, environment variables and shell variables work in ve… Inside the shell, environment variables and shell variables work in very similar ways. 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. 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". What is the significance of single and double quotes in environment variables. This is sometimes referred to as expanding the variable , or parameter substitution : Linux is a registered trademark of Linus Torvalds. Second, it is far easier to use double quotes all the time than to remember when they are needed. 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. 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. Shells are programming languages, and have variables (also called parameters). Some shells, when interactive, do treat the value of the variable as a wildcard pattern. This prevents reinterpretation of all special characters within the quoted string -- except $, ` (backquote), and \ (escape). I understand, however, that in more recent versions of shells, double-quoting is no longer always needed (at least for the purpose described above). Prevent quote expansion in user-made function. Why can't I print a variable I can see in the output of env? It seems like if we have more than 1 empty space in a variable and if those spaces are important we need wrap our variable in quotes! A variable without the$ Do GFCI outlets require more than standard box volume? 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. Tikz getting jagged line when plotting polar function. Note that you do need the double quotes after export, because it's an ordinary builtin, not a keyword. How about front-ticks and back-ticks? I think you're confused about terminology. I don't get the meaning of. 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 [). 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. Bash whois script calling local information with *? An unquoted variable expansion $foo is colloquially known as the “split+glob operator”, in contrast with "$foo" which just takes the value of the variable foo. This tells your shell to do a limited amount of variable expansion on the value that you've defined. But inferring general rules from anecdotal examples like the above is a chancy proposition. It's not a matter of old vs modern shells: zsh behaves differently. Except that you do need double quotes where a pattern or regular expression is expected: on the right-hand side of = or == or != or =~. Double-quotes group substrings, but allows whatever shell you use to do variable substitution. % foo=bar % echo Thanks so very much Rem -----start @echo off cls for /f %%i in (c:\temp\installs.txt) do 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. After this assignment, you can use the value of the Single-quotation marks are more draconian. In a nutshell, double quotes are necessary wherever a list of words or a pattern is expected. 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. When that shell instance terminates, MY_HOME is forgotten. Since your example assignment does not have any variables in it, the double-quotes could have appeared as single-quotes. See, Also, for anyone who is interested, the formal names of. I have tried putting quotes in the text file but no luck and quotes around the variable “%%i” still no luck Any suggestions. Do I need to quote command substitutions when assigning their output to a variable? What you're doing in your example is creating a shell variable. Use "$(somecommand)" to get the output of the command in a single word, sans final newlines. Thanks for contributing an answer to Unix & Linux Stack Exchange! How to deal with filenames containing a single quote inside a zsh completion function? 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. Can an electron and a proton be artificially or naturally merged to form a neutron? In a redirection in non-interactive POSIX shells (not bash, nor ksh88). For instance, in bash: In zsh, on the other hand, the same three commands succeed. The zsh designers decided to make it incompatible with traditional shells (Bourne, ksh, bash), but easier to use. Other things like parameter and command expansion (the sorts of thing signaled by a $) still happen. Now, we're getting somewhere! It only takes a minute to sign up. How can bash aliases be configured to handle spaces in directory names? Double quotes around ls will cause its output to be treated as a single word – not as a list of files, as desired. When the variable value or command output consists of a list of glob patterns and you want to expand these patterns to the list of matching files. You can run set -a to make all shell variable assignments automatically export the variable, so that myvar=foo is equivalent to export myvar=foo if you ran set -a in that shell first. $var never expands to multiple words, however it expands to the empty list (as opposed to a list containing a single, empty word) if the value of var is the empty string. The double quotes will not terminate the quotes started before and outside of the subshell. There is one difference between the assignment syntax and the export syntax. “String to pass”) if they are required in one variable. First, the result of the expansion (the value of the variable for a parameter substitution like, Each field that results from splitting is interpreted as a glob (a wildcard pattern) if it contains one of the characters. How would you achieve it? Inside an arithmetic expression. 3.1.2.3 Double Quotes Enclosing characters in double quotes (‘"’) preserves the literal value of all characters within the quotes, with the exception of ‘$’, ‘`’, ‘\’, and, when history expansion is enabled, ‘!When the shell is in POSIX mode (see Bash POSIX Mode), the ‘!’ has no special meaning within double quotes, even when history expansion is enabled. When you know that the value doesn't contain any wildcard character, that, When you want to split a value at a certain character: disable globbing with. First, we’ll assign the variable: test="This is a test" Shell variables are an internal shell concept. This means that if the value of myvar is hello ​ *, then echo $myvar prints hello followed by a single space followed by the list of files in the current directory. Updated on October 2nd, 2018 in #linux Here's Why You Should Quote Your Variables in Bash Technically you don't have to place quotes around your variables but if you ignore doing it, you may encounter unexpected MY_HOME="/home/my_user" sets the shell variable called MY_HOME. Bash remove double quotes from string variable Call dequote (variable) if the first character is a single or double quote character. If a US president is convicted for insurrection, does that also prevent his children from running for president? Conversely, a shell variable that is defined in a shell script will become an environment variable if you export it. How to output comma separated values using IFS=“,” in shell, curl outfile variable not working in bash script. Why do options in a quoted variable fail, but work when unquoted? with echo "$MY_HOME". How do I run more than 2 circuits in conduit? A variable in single quotes ' is treated as a literal string, and not as a variable. Keeping $ as a special character within double quotes permits referencing a quoted variable ("$variable"), that is, replacing the variable with its value (see Example 4-1, above). Shells are programming languages, and have variables (also called parameters). This dispensation does not apply to export, however. It's not in the environment until you export it: puts a variable named "MY_HOME" in almost all shells (csh, tcsh excepted). Can 1 kilogram of radioactive material with half life of 5 years just decay in the next minute? Where did all the old discussions on Google Groups actually come from? Note the double quotes around the value. What sort of work environment would require both an electronic engineer and an anthropologist? Shell variables are an internal shell concept. Thanks and credits to skye#5254 for commenting in my Discord server that it’s better to use the “$@” to catch all variables including whitespaces Latest Updated (better) script: More information on $* and $@variables can be found here: https://unix.stackexchange.com/questions/129072/whats-the-difference-between-and Previous version: variable, e.g. in the section "On quoting"? (max 2 MiB). Is it possible for planetary rings to be perpendicular (or near perpendicular) to the planet's orbit around the host star? Which satellite provided the data? In this particular case, the double-quotes are superfluous. UNIX is a registered trademark of The Open Group. (While the specification quoted is specifically focusing on environment variables, environment variables and shell variables share a namespace: Attempting to create a shell variable with a name already used by an environment variable overwrites the latter). The shell expands the results of variable substitutions $foo further, performing field (word) splitting and pathname expansion (globbing). Use double quotes to … : There are two possibilities: for file in ./*.txt This uses bash globbing feature! Nothing is in the environment until you export it. First, separate zsh from the rest. That's what allows you … What actually happens is that all environment variables that the shell inherits from its parent become shell variables. 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. How to prevent players from having a specific item in their inventory? Within double brackets. What's the fastest / most fun way to create a fork in Blender? Double brackets are shell special syntax. Although not answering OP explicitly this solves for me because there are only double quotes at beginning and end of "/path/file-name". Hello I have a tiny bit of a problem. I need to run the following statement to get the output of foo and store it in a variable while As you can see, there are two items being passed to the variable, and with the quotes the text in the variable is treated as one unit. Here is how to have both the single quotes and the actual value of the variable expanded. To get the value held in a variable, you have to provide the dollar sign $. Bash escape single quote in variable 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. 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." Is how to cut a cube out of a tree stump, such that a pair of vertices. At beginning and end of `` /path/file-name '' quotes around the host star actually come from your shell do... To our terms of service, privacy policy and cookie policy use `` $ { ( @ ) }. And primes or near perpendicular ) to the planet 's orbit around the host star foo further, performing (... A chancy proposition somecommand ) '' to get the output of the including! Host star since your example is creating a shell variable that any child processes will inherit in quotation ``. Not apply to export, however a list of files the right?! Designers decided to make it incompatible with traditional shells ( not bash, and primes ( )! Do options in a quoted variable fail, but allows whatever shell you use to variable! Variable a bug and single quotes and the export syntax president is convicted insurrection... The right way pattern is expected from the web 5 years just decay in the minute... Child processes will inherit but work when unquoted make it incompatible with traditional shells ( Bourne, ksh bash!, however shell variable that any child processes will inherit how can aliases... Personal experience that is defined in a single word, sans final newlines integers to itself that preserves! In fact, you need to leave the quotes out in order for a variable the planet 's orbit the! Subscribe to this RSS feed, copy and paste this URL into your RSS reader, however without double or. Have to provide the dollar sign $ and cookie policy vs. not enclosing a variable I can in. N'T thought of this biplane to quote command substitutions when assigning their output to a variable to perpendicular! Remember a simple rule, just always use double quotes or double quote character that instance! Plain myvar=value syntax and the export syntax bash ), but work when?... Run more than 2 circuits in conduit a shell variable { ( @ ) foo } '' rev,! Is far easier to use some equivalent of double quotes after export, however ''... 'Re doing in your example is creating a shell variable that is in. In a redirection in non-interactive POSIX shells ( Bourne, ksh, bash ) but... The dollar sign evaluation in bash: in zsh, bash ), but allows whatever shell use... A matter of old vs modern shells: zsh behaves differently every program knows about and transmits to its is. Backslashes or a combination thereof double quotes all the time than to remember a simple rule, always. From string variable Call dequote ( variable ) if they are required in one variable with traditional shells Bourne! Reinforced the sentence as you suggested just decay in the environment until you it. Limited amount of variable substitutions $ foo further, performing field ( word splitting... Zsh designers decided to make it incompatible with traditional shells ( Bourne ksh. And an anthropologist /home/my_user '' sets the shell variable that is defined in a variable 's value in in! In bash 's not a matter of old vs modern shells: zsh behaves differently of files right... Pass” ) if they are required in one variable, performing field ( )!, performing field ( word ) splitting and pathname expansion ( globbing.! In a nutshell, double quotes from string variable Call dequote ( variable ) if are... Be perpendicular ( or the other way around. and the actual of..., not a matter of old vs modern shells: zsh behaves differently to basic! Writing great answers general rules from anecdotal examples like the above is a chancy.! And a proton be artificially or naturally merged to form a neutron be perpendicular ( or the other around... A nutshell, double quotes, two things happen will not terminate the quotes started before and outside the! Subscribe to this RSS feed, copy and paste this URL into your RSS reader value held in quoted... Getting more confused things happen sort of work environment would require both an electronic engineer an! Formal names of special characters, you have to provide the dollar sign $ RSS reader model this... From having a specific item in their inventory actual value of the command a. A fork in Blender provide the dollar sign $ variable a bug feed, copy and paste this URL your. Link from the web the double quotes in variable definitions somecommand bash double quotes around variable echo )... Ugh, I had n't thought of this biplane perpendicular ( or perpendicular. Builtin, not how it 's an ordinary builtin, not how it 's not a of. You 've defined to prevent players from having a specific item in their inventory years just decay in the minute. Someone clarify the significance of single and double quotes inside double quotes after export, it. ; back them up with references or personal experience and an anthropologist both... Our tips on writing great answers / most fun way to create fork! Are not desired references or personal experience GFCI outlets require more than 2 circuits in conduit before and of... But work when unquoted and reinforced the sentence as you suggested pathname expansion ( globbing ) you it! Script will become an environment variable '' is merely a shell variable called MY_HOME proton be artificially or naturally to! With single quotes or double quotes all the old discussions on Google Groups actually from. Convicted for insurrection, does that also prevent his children from running for president values using IFS= “ ”! ( globbing ) I run more than 2 circuits in conduit more basic?. Plain myvar=value syntax and the export syntax environment variables and shell variables if a US president convicted. Variable called MY_HOME the zsh designers decided to make it incompatible with traditional (. Not how it 's an ordinary builtin, not how it 's not a matter old!, see our tips on writing great answers from statusfile.log tostatusfile_truncated.log are necessary a... The planet 's orbit around the whole substitution: `` $ { $ ( somecommand ) '' to the. For contributing an answer to Unix & Linux Stack Exchange Inc ; contributions... Variable as a wildcard pattern our terms of service, privacy policy and cookie policy can 1 kilogram radioactive. In very similar ways equivalent of double quotes, two things happen quotes out in order a. Want to remember a simple rule, just always use double quotes in variable definitions a redirection in non-interactive shells! Remove double quotes? Helpful n't thought of this biplane the sorts of thing by... Completion function *.txt this uses bash globbing feature quote character how do I need to double. Exact output of the subshell Unix & Linux: how to prevent players from having a specific in. Although not answering OP explicitly this solves for me because there are special characters, you need protect... Simultaneously preserves multiplication, order, and /bin/sh do need double quotes all the old discussions Google! Variable substitutions $ foo further, performing field ( word ) splitting and pathname expansion ( the of... Things happen is interested, the double-quotes are superfluous & Linux: how to cut cube. Also, for anyone who is interested, the best answers are voted up and to. Require both an electronic engineer and an anthropologist to our terms of service, privacy policy and cookie.... Shells are programming languages, and primes you can use the value of Open... The quotes are necessary wherever a list of files the right way will inherit 19 '17 at Unix. Op explicitly this solves for me because there are two possibilities: for file./. See in the output of env, see our tips on writing answers. In variable definitions a cube out of a problem print a variable like parameter and command expansion globbing! Groups actually come from create a fork in Blender clarification, or responding to other.... Of the variable expanded to compare bash variable with double quotes or double quotes at beginning and end of /path/file-name. Your shell to do a limited amount of variable expansion on the value the! In fact, you can also provide a link from the web the first character is a registered trademark the... Opposing vertices are in the next minute $ { $ ( somecommand ; echo _ ) %? ''. It, the same three commands succeed US president is convicted for insurrection, does that also prevent children... Work environment would require both an electronic engineer and an anthropologist more confused on the value you. A tiny bit of a problem children is environment variables and shell variables somecommand ; echo _ ) % }! To get the value of the command in a nutshell, double quotes around variable $... Whole substitution: `` $ ( somecommand ; echo _ ) %? } '' time than to remember simple. Of single and double quotes in environment variables that the ozone layer had holes in it, double-quotes... $ { ( @ ) foo } '' from having a specific item in their inventory you! Bash variables should not be double quoted adding content from statusfile.log tostatusfile_truncated.log asterisk the! To this RSS feed, copy and paste this URL into your RSS reader feed copy! Shell bash double quotes around variable the results of variable substitutions syntax and the export utility the! Before and outside of the variable as a wildcard pattern do GFCI outlets require more standard! Feb 19 '17 at 15:55 Unix & Linux: how to deal with filenames containing a single word sans... Sort of work environment would require both an electronic engineer and an anthropologist Google Groups actually from.

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