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For example, I want to create an alias to remove duplicate lines:

alias rm.dup  'perl -ne 'print unless $dup{$_}++;''

When source .cshrc, it reports: "dup: Undefined variable."

If change it to

alias rm.dup  'perl -ne 'print unless \$dup{$_}++;' \!* &'

It reports: "!* &: Command not found."

And also tried 

alias rm.dup  'perl -ne 'print unless \$dup{$_}++;''

Reports: ": Command not found."

What's the general rule of using variable with alias?

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1 Answer 1

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alias rm.dup  'perl -ne '\''print unless $dup{$_}++'\'' \!* &'

Since one cannot embed a single quote within single quotes, so one way is to break out of the single quote, slip in a literal quote, then restart the quotes.

'perl -ne '\''print unless $dup{$_}++'\'' \!* &'
|---------|B |-----------------------|D |------|
     A                   C                  E

Another way is:

alias rm.dup  'perl -ne "print unless "\$"dup{"\$"_}++" \!* &'
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