Chapter 10: Expansions and Substitutions

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Tilde Expansion

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• ~ represents $HOME environment variable
• ~- represents $OLDPWD, and will show the previous directory you were in (if you had recently changed directories).

Brace Expansion

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It is used to generate strings at the command line or in a shell script. For example, touch file{0..12} will create file1, file2,.., file12.

Parameter Expansion

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We’ve seen this while reading variables - parameter expansion lets us recall stored values:

1 a="Hello World"
2 echo ${a}
3 echo $a

Pattern Substitution

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It is a special case of parameter expansion.

1 greeting="hello there"
2 # will replace there with everybody
3 echo ${greeting/there/everybody}

Command Substitution

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Allows us to use the output of a command within another command. For example,
echo "$(uname -r)".