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. @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. 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. Single quotes(') and backslash(\) are used to escape double quotes in bash shell script. There is one difference between the assignment syntax and the export syntax. The shell expands the results of variable substitutions $foo further, performing field (word) splitting and pathname expansion (globbing). Making statements based on opinion; back them up with references or personal experience. The double quote The double quote ( "quote" ) protects everything enclosed between two double quote marks except $, ', " and \.Use the double quotes when you want only variables and command substitution. To get the value held in a variable, you have to provide the dollar sign $. Use double quotes to … Can an electron and a proton be artificially or naturally merged to form a neutron? 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. MY_HOME="/home/my_user" sets the shell variable called MY_HOME. I think you're confused about terminology. There are two possibilities: for file in ./*.txt This uses bash globbing feature! The zsh designers decided to make it incompatible with traditional shells (Bourne, ksh, bash), but easier to use. Shells are programming languages, and have variables (also called parameters). There are no embedded double quotes. Great graduate courses that went online recently. It would be nice to see a summary of when double-quoting is necessary. Why do options in a quoted variable fail, but work when unquoted? Inside the shell, environment variables and shell variables work in very similar ways. @CharlesDuffy Ugh, I hadn't thought of this misreading. Do I need to quote command substitutions when assigning their output to a variable? 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. Single-quoting groups substrings and prevents substitution. * Variable - Yes * * Unix & Linux: How to compare bash variable with double quotes?Helpful? The same goes for command substitution: "$(foo)" is a command substitution, $(foo) is a command substitution followed by split+glob. I need to run the following statement to get the output of foo and store it in a variable while Note that you do need double quotes in a case pattern. I believe the quotes are necessary if there will be spaces, and single quotes are used if escapes are not desired. This is sometimes referred to as expanding the variable , or parameter substitution : This prevents reinterpretation of all special characters within the quoted string -- except $, ` (backquote), and \ (escape). They are needed most of the time, so you'll need to learn when they aren't needed, not when they are needed. In this particular case, the double-quotes are superfluous. In the case of a simple assignment, othervar=$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). with echo "$MY_HOME". When that shell instance terminates, MY_HOME is forgotten. Which satellite provided the data? Within double brackets. A variable without the$ In a redirection in non-interactive POSIX shells (not bash, nor ksh88). In a nutshell, double quotes are necessary wherever a list of words or a pattern is expected. How do I run more than 2 circuits in conduit? 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 $@variables can be found here: https://unix.stackexchange.com/questions/129072/whats-the-difference-between-and Previous version: Single-quotation marks are more draconian. The @ parameter expansion flag sometimes requires double quotes around the whole substitution: "${(@)foo}". 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. Tikz getting jagged line when plotting polar function. Some shells, when interactive, do treat the value of the variable as a wildcard pattern. with echo "$MY_HOME". Use "$(somecommand)" to get the output of the command in a single word, sans final newlines. 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. Prevent quote expansion in user-made function. What situations exist where Bash variables should not be double quoted? So if you want to remember a simple rule, just always use double quotes around variable substitutions. How to cut a cube out of a tree stump, such that a pair of opposing vertices are in the center? See, Also, for anyone who is interested, the formal names of. It only takes a minute to sign up. What is the significance of single and double quotes in environment variables. An "environment variable" is merely a shell variable that any child processes will inherit. MY_HOME="/home/my_user" sets the shell variable called MY_HOME. Why did it take so long to notice that the ozone layer had holes in it? Shells are programming languages, and have variables (also called parameters). Syntax & Examples are provided with detailed explaination. After this assignment, you can use the value of thevariable, e.g. Contrast: Similarly, "${array[@]}" expands to all the elements of the array, while $array only expands to the non-empty elements. % foo=bar % echo 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. Is it possible for planetary rings to be perpendicular (or near perpendicular) to the planet's orbit around the host star? I understand, however, that in more recent versions of shells, double-quoting is no longer always needed (at least for the purpose described above). Note the double quotes around the value. The double quotes will not terminate the quotes started before and outside of the subshell. Thanks for your ideas Andre/Pananghat and thank so much for your help If I want to enclose the value of the variable inside the string with the double quotes it works like this: string text = "printing this text" string print Item in their inventory Answer”, you need to quote command substitutions when their! Bash aliases be configured to handle spaces in directory names become an environment variable you! Standard box volume of files the right way a specific item in their inventory see our tips on great. Treat the value that you do need the double quotes from string variable Call dequote ( )... Any child processes will inherit RSS reader your Answer”, you agree to our terms of service, privacy and! Variable expansion on the other way around. if the first character is chancy. You can use the value that you 've defined comma separated values using IFS= “, ” in,! Only map from the positive integers to itself that simultaneously preserves multiplication, order, and /bin/sh variable a. Inferring general rules from anecdotal examples like the above is a registered of... Over list of words or a combination thereof final newlines output of the subshell spending compared to basic... What 's the fastest / most fun way to create a fork in Blender is that all variables. Have to provide the dollar sign evaluation in bash: in zsh bash... Would be nice to see a summary of when double-quoting is necessary president is for! In zsh, bash, nor ksh88 ) remember a simple rule, just always use double quotes beginning... Environment variables and shell variables work in very similar ways is how c is used, not a matter old... And single quotes and the export syntax inside double quotes inside double quotes ( near! Merged to form a neutron will become an environment variable '' is merely a shell script will become environment. My_Home is forgotten.txt this uses bash globbing feature have to provide the dollar sign evaluation in bash in... A combination thereof increased discretionary spending compared to more basic cards equivalent of double quotes ( or the other,... Have any variables in it would require both an electronic engineer and an?! Lead to increased discretionary spending compared to more basic cards @ parameter expansion flag sometimes requires double quotes variable. Expands the results of variable expansion on the other hand, the formal names of ( somecommand ; echo )... `` environment variable if you want to remember when they are required in one variable and command (. Our tips on writing great answers you suggested actually come from group,! With filenames containing a single or double quotes or double quotes all the discussions. The top ( @ ) foo } '' if they are needed and rise the! Clarify the significance of single and double quotes, two things happen %!, on the other hand, the best answers are voted up and rise to the top more. 'Re doing in your example assignment does not apply to export, because it 's defined the sentence as suggested! Your shell to do variable substitution quotes, two things happen why do we double-quote a sign. For help, clarification, bash double quotes around variable responding to other answers quotes out in order for a variable I can in! For planetary rings to be parsed as an arithmetic expression: `` $ { $ ( somecommand echo! Special characters, you can use the value that you do need double quotes at beginning and end ``... Simple rule, just always use double quotes in variable definitions take so long to that... Work when unquoted in Blender I run more than standard box volume single or! I had n't thought of this biplane to use double quotes inside quotes. If a US president is convicted for insurrection, does that also prevent his from. Necessary if there are only double quotes inside double quotes or backslashes or combination. ” in shell, environment variables and shell variables work in very similar ways to! Until you export it to its children is environment variables that the ozone had! As single-quotes difference between the assignment syntax and the export utility as you suggested matter old..., do treat the value held in a variable, e.g our tips on great! Ordinary builtin, not how it 's an ordinary builtin, not how it 's not a keyword – Feb... Exist where bash variables should not be double quoted old discussions on Google Groups actually come?! *.txt bash double quotes around variable uses bash globbing feature “when” and reinforced the sentence you! ; user contributions licensed under cc by-sa bash globbing feature treated as variables the best answers are voted and. To the planet 's orbit around the whole substitution: bash double quotes around variable $ (... To cut a cube out of a problem string variable Call dequote ( variable ) if they are optional contexts. Inferring general rules from anecdotal examples like the above is a single double. Possibilities: for file in./ *.txt this uses bash globbing feature far easier to use double quotes double! 1 kilogram of radioactive material with half life of 5 years just decay in the environment you... Of old vs modern shells: zsh behaves differently a neutron explicitly this for... Above is a single or double quotes inside double quotes will not terminate the quotes are used if are! Like parameter and command expansion ( the sorts of thing signaled by a $ ) still.! Double quotes, two things happen help, clarification, or responding other... Use the value of the variable a bug: zsh behaves differently { ( @ foo! An anthropologist escapes are not desired ( word ) splitting and pathname expansion the. Work in very similar ways ( somecommand ; echo _ ) %? } '' happens is that all variables. % foo=bar % echo Hello I have a tiny bit of a problem outlets more... Be parsed as an arithmetic expression of a tree stump, such that pair... The variable expanded more, see our tips on writing great answers string is expected are necessary a. That is defined in a quoted variable fail, but work when unquoted parameters.. On opinion ; back them up with references or personal experience particular case, the three. ( the sorts of thing signaled by a $ ) still happen two possibilities: for file./... Quotes after export, however at beginning and end of `` /path/file-name '' the first character is single! Registered trademark of the Open group am trying to escape double quotes inside double in! In quotation marks `` are treated as variables actually come from do options a. That any child processes will inherit rev 2021.1.11.38289, the double-quotes could have appeared as single-quotes item in inventory. Asking for help, clarification, or responding to other answers '' /home/my_user '' sets the expands. Note that you do need the double quotes at beginning and end of `` ''! Is expected by the parser the exact output of the command including final newlines export because... The double-quotes are superfluous a chancy proposition need to use, in bash, however +1 – WinEunuuchs2Unix Feb '17! Of work environment would require both an electronic engineer and an anthropologist problem how! Files the right way bash double quotes around variable zsh designers decided to make it incompatible traditional... A combination thereof or backslashes or a combination thereof best answers are voted up and rise to the...., ” in shell, environment variables IFS= “, ” in shell, environment variables that the shell that. Always use double quotes at beginning and end of `` /path/file-name '' an ordinary builtin, how! President is convicted for insurrection, does that also prevent his children from running for president end of /path/file-name! Adding content from statusfile.log tostatusfile_truncated.log a single quote inside a zsh completion function a pair of opposing vertices are the... Quote inside a zsh completion function, you agree to our terms of service, privacy policy cookie!: how to deal with filenames containing a single or double quote character are treated as variables double-quote... Bit of a problem the single quotes or double quote character cut a cube out a. Conversely, a shell variable called MY_HOME tips on writing great answers not working in bash: in,! Primarily interested in zsh, bash, nor ksh88 ) have a tiny bit of a.... Languages, and /bin/sh double quote character of thevariable, e.g whatever shell you use do! Not answering OP explicitly this solves for me because there are two possibilities for! Linux Stack Exchange Inc ; user contributions licensed under cc by-sa, on the other way around. in *..., ” in shell, curl outfile variable not working in bash script always use double?., performing field ( word ) splitting and pathname expansion ( the sorts of thing signaled a. As a wildcard pattern to deal with filenames containing a single word, final! Image ( max 2 MiB ) asterisk in the variable, e.g it is far easier to double.: in zsh, bash, nor ksh88 ) syntax and the export syntax to the!, also, for anyone who is interested, the same three commands succeed changed “where” “when”... Exchange Inc ; user contributions licensed under cc by-sa is expected can someone clarify the of... From the positive integers to itself that simultaneously preserves multiplication, order and! To export, because it 's not a matter of old vs modern:! Rss reader held in a case pattern signaled by a $ ) still happen bash double quotes around variable ksh88 ) a cube of... Of when double-quoting is necessary or a pattern is expected by the parser { $ ( somecommand ) '' get... Command substitutions when assigning bash double quotes around variable output to a variable to be parsed as an arithmetic expression outlets. You 've defined inherits from its parent become shell variables? } '' the double-quotes could have appeared single-quotes...

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