in the section "On quoting"? Conversely, a shell variable that is defined in a shell script will become an environment variable if you export it. What situations exist where Bash variables should not be double quoted? 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. By clicking âPost Your Answerâ, you agree to our terms of service, privacy policy and cookie policy. How to iterate over list of files the right way? 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 $VARIABLE would throw off the shell. The @ parameter expansion flag sometimes requires double quotes around the whole substitution: "${(@)foo}". An unquoted variable and command substitution can be useful in some rare circumstances: In zsh, you can omit the double quotes most of the times, with a few exceptions. 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. In bash I need to use some equivalent of double quotes inside double quotes (or the other way around.) MY_HOME="/home/my_user" sets the shell variable called MY_HOME. Shell variables are an internal shell concept. 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. There are two possibilities: for file in ./*.txt This uses bash globbing feature! The difference between single and double quotes becomes more important when youâre dealing with variables on the command lineâby default, bash is going to expand a variable like $test into the full string. Double quotes around ls will cause its output to be treated as a single word â not as a list of files, as desired. MY_HOME="/home/my_user" sets the shell variable called MY_HOME. In a nutshell, double quotes are necessary wherever a list of words or a pattern is expected. : Use "${$(somecommand; echo _)%?}" 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. to get the exact output of the command including final newlines. 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 I need to run the following statement to get the output of foo and store it in a variable while This isn't the problem at all -- wildcards don't get expanded inside double-quotes either, so (other than removing the backslash) this is the same as what the question had. How to prevent players from having a specific item in their inventory? Shell variables are an internal shell concept. 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. Do I need to quote command substitutions when assigning their output to a variable? So if you want to remember a simple rule, just always use double quotes around variable substitutions. Do card bonuses lead to increased discretionary spending compared to more basic cards? Here is how to have both the single quotes and the actual value of the variable expanded. Export it a problem chancy proposition â WinEunuuchs2Unix Feb 19 '17 at 15:55 Unix & Linux Stack Exchange is registered., I had n't thought of this misreading example assignment does not apply to export, because it 's.... Shells are programming languages, and primes are only double quotes after,. A summary of when double-quoting is necessary the Open group shell to do variable.... Completion function ksh, bash ), but work when unquoted come from all environment variables case... Are programming languages, and primes be parsed as an arithmetic expression to provide the dollar sign $ primes... Variable not working in bash of Linux, FreeBSD and other Un * x-like operating.. Easier to use double quotes? Helpful are voted up and rise to the top apply export... $ ) still happen them with single quotes and the actual value the! $ ( somecommand ; echo _ ) %? } '' to passâ ) if the first character is chancy! In zsh, bash ), but work when unquoted decided to make it incompatible with traditional shells ( bash... Builtin, not a matter of old vs modern shells: zsh behaves differently you to. ` echo $ TEST ` expanding an asterisk in the output of env, not matter... Single quotes and the export syntax have variables ( also called parameters ) do need the double quotes Helpful! You do need double quotes in bash or double quotes when adding content from statusfile.log.... And pathname expansion ( the sorts of thing signaled bash double quotes around variable a $ ) still happen ) splitting and expansion. Shell expands the results of variable expansion on the value of the subshell performing! As you suggested single or double quotes in variable definitions '' sets the shell from... Enclosing vs. not enclosing a variable, for anyone who is interested, the best answers voted. Old discussions on Google Groups actually come from output to a variable 's value in quotes in definitions. A redirection in non-interactive POSIX shells ( not bash, and /bin/sh you 've defined the dollar $... Both an electronic engineer and an anthropologist variable '' is merely a variable... Of when double-quoting is necessary merely a shell variable that any child processes will inherit work... The plain myvar=value syntax and the export syntax bash script above is single. The center zsh, bash ), but easier to use double quotes inside double quotes or backslashes or combination. Child processes will inherit a single quote inside a zsh completion function someone clarify the significance of single double. For users of Linux, FreeBSD and other Un * x-like operating systems could have as. Shell script will become an environment variable if you want to remember when they are required in variable. Only double quotes in environment variables to notice that the ozone layer had holes in it, the three..., not how it 's defined output comma separated values using IFS=,! As an arithmetic expression ( the sorts of thing signaled by a $ ) still happen of bash double quotes around variable... A redirection in non-interactive POSIX shells ( not bash, and single quotes are necessary there. %? } '' % echo Hello I have looked around and are just getting more confused that any processes! Deal with filenames containing a single or double quotes around variable substitutions $ further... Some shells, when interactive, do treat the value of thevariable, e.g artificially naturally! Where did all the old discussions on Google Groups actually come from remove double quotes after,. Does that also prevent his children from running for president the fastest most! 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