Shell Scripts – Naming Conventions for Variables

bashshellshell-scriptvariable

Most languages have naming conventions for variables, the most common style I see in shell scripts is MY_VARIABLE=foo. Is this the convention or is it only for global variables? What about variables local to the script?

Best Answer

Environment variables or shell variables that are introduced by the operating system, shell startup scripts, or by the shell itself etc. are usually all in CAPITALS.

To prevent your own variables from conflicting with these variables, it is a good practice to use lower_case variable names.

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Bash – Sharing variables across multiple shell scripts

When you run scripts 1-3 inside your main script, they are each run inside their own sub-shell, which is why they don't recognise the variables defined in their parent shell. Use export to make variables available to sub-shells:

#!/bin/sh
export var1="1"
export var2="2"
bash script1.sh
bash script2.sh
bash script3.sh

An alternative (relevant for your second question) would be to pass the variables to the scripts as positional parameters:

#!/bin/sh
var1="1"
var2="2"
bash script1.sh "$var1" "$var2"
bash script2.sh "$var1" "$var2"
bash script3.sh "$var1" "$var2"

Inside scripts 1-3, these variables would then be available as $1 and $2 respectively.

Shell – Setting variables from shell: how to use them in a script

export foo=bar will set the global variable $foo to bar. You can also use foo=bar ./test.sh as a single command to set foo to bar for test.sh.

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Related Solutions

Bash – Sharing variables across multiple shell scripts

Shell – Setting variables from shell: how to use them in a script

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