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'eval' used in variable assignment


 
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# 1  
'eval' used in variable assignment

Code:
pattern1=book
{
x=1
eval echo \$pattern$x
}
book  (this is the output)

But when I assign a variable to the output of the eval it doesn't work unless I prefix 2 times backslash before $ as shown below.

Code:
{
a=`eval echo \\$pattern$x`
echo $a
}
book

Why here twice "\" has to be prefixed.
# 2  
The first time is when bash sees the \ it needs to be escaped: \\. The next requirement is for eval, where bash needs to see \$ so the value "$pattern" is actually seen by the shell that eval runs.
# 3  
It's not necessary to double the backslash when using the modern command substitution syntax, $( ... ), instead of the old, deprecated, and more complicated backtick syntax, ` ... `.

Regards,
Alister
# 4  
eval is not necessary here, fortunately.

Code:
read $pattern$x <<EOF
variablecontents
EOF


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