Shell Script – How to Use ‘ in Alias?

aliasescape-charactersquotingshell-script

I have one-line that I want to call using alias.

while printf '%s ' "$(df -P / | awk 'NR==2 { print $(NF-1) }')"; do sleep 30; done

I tried to escape ' like \' but it didn't work.

What is the correct syntax to use above one-liner in alias?

Best Answer

alias my_du=$'while printf \'%s \' "$(df -P / | awk \'NR==2 { print $(NF-1) }\')"; do sleep 3; done'

You can check the result with

alias my_du

If $() is quoted by " instead of ' or \ then it is substituted and the result rather than the intended program call becomes part of the alias definition.

Related Solutions

When to Use Bash ANSI C Style Escape, e.g. $’\n’

You use $'...' when you want escape sequences to be interpreted by the shell.

$ echo 'a\nb'
a\nb

$ echo $'a\nb'
a
b

In perl, -e option get a string. If you use $'...', the escape sequences in string are interpreted before passing to perl. In your case, \r had gone and never passed to perl.

With $'...':

$ perl -MO=Deparse -we $'binmode STDIN;undef $/;$_ = <>;if(/ab\r\ncd/){print "test"}'
BEGIN { $^W = 1; }
binmode STDIN;
undef $/;
$_ = <ARGV>;
if (/ab\ncd/) {
    print 'test';
}
-e syntax OK

Without it:

$ perl -MO=Deparse -we 'binmode STDIN;undef $/;$_ = <>;if(/ab\r\ncd/){print "test"}'
BEGIN { $^W = 1; }
binmode STDIN;
undef $/;
$_ = <ARGV>;
if (/ab\r\ncd/) {
    print 'test';
}
-e syntax OK

Environment Variables – How to Save an Alias of an Eval Command

Enclose your alias in single quotes instead of double quotes.

alias dockereval='eval $(docker-machine env)'

Double quotes allow expansion of variable (in bash at least) while single quotes don't

Best Answer

Related Solutions

When to Use Bash ANSI C Style Escape, e.g. $’\n’

Environment Variables – How to Save an Alias of an Eval Command

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