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bash substitution default

Jason M Potter answered on September 21, 2022 Popularity 3/10 Helpfulness 1/10

answer bash substitution default

bash substitution default

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## Bash Substitution - Default Values
${parameter-default}, ${parameter:-default}
## If parameter not set, use default.

var1=1; var2=2;
# var3 is unset.

echo ${var1-$var2}   # 1
echo ${var3-$var2}   # 2
#           ^          Note the $ prefix.

echo ${username-`whoami`}
# Echoes the result of `whoami`, if variable $username is still unset.

## ${parameter-default} and ${parameter:-default} are almost equivalent. 
## : makes a difference only when parameter has been declared, but is null.

Popularity 3/10 Helpfulness 1/10 Language shell

Source: tldp.org

Tags: bash default shell substitution

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Contributed on Sep 21 2022

Jason M Potter

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