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What is VAR in shell script?
A variable is a character string to which we assign a value. The value assigned could be a number, text, filename, device, or any other type of data. A variable is nothing more than a pointer to the actual data. The shell enables you to create, assign, and delete variables.
How do you know if a string is nonzero?
If you want to know if a variable is non-zero length, do any of the following:
- quote the variable in single brackets (column 2a)
- use -n and quote the variable in single brackets (column 4a)
- use double brackets with or without quoting and with or without -n (columns 1b – 4b)
When to use$ VAR and$ var2?
$ {VAR} and $VAR are exactly equivalent. For a plain variable expansion, the only reason to use $ {VAR} is when parsing would otherwise grab too many characters into the variable name, as in $ {VAR1}_$VAR2 (which without braces would be equivalent to $ {VAR1_}$VAR2 ).
What’s the difference between Var and VAR1 in POSIX?
VAR=$VAR1 is a simplified version of VAR=$ {VAR1}. There are things the second can do that the first can’t, for instance reference an array index (not portable) or remove a substring (POSIX-portable). See the More on variables section of the Bash Guide for Beginners and Parameter Expansion in the POSIX spec.
How to use quotes around a variable in Bash?
See the More on variables section of the Bash Guide for Beginners and Parameter Expansion in the POSIX spec. Using quotes around a variable as in rm — “$VAR1” or rm — “$ {VAR}” is a good idea.
Which is the definitive reference for Bash shell scripting?
The definitive reference for Bash shell scripting is the libre online reference, TLDP The Linux Documentation Project https://www.tldp.org/LDP/abs/html/parameter-substitution.html Some times you have to use $ {var} instead of $var when you parse data from user input say in website to server to be executed $var won’t work for example