How to expand variable literally when calling perl from csh script?

Question

Below is a csh script.

#! /bin/csh
set alpha=10\20\30;
set beta = $alpha.alpha;
perl -p -i.bak -e 's/gamma/'$beta'/' tmp;

The tmp file contains just the word gamma. After running tmp.csh, I expect 10\20\30.alpha in tmp, but it's now 102030.alpha.

How to preserve slashes in this situation?

Note: I wouldn't prefer changing definition of alpha variable, as it is used in the script else where where it needs to be in this format (10\20\30) only.

Thanks.

Jim Black · Accepted Answer · 2013-03-29 17:47:42Z

2

In csh, for your alpha assignment, the backslash is being taken to mean 'a literal 2 or 3'. In order to keep csh from doing this, the assignment needs to be enclosed in quotes.

#! /bin/csh
set alpha="10\20\30";
set beta = $alpha.alpha;
perl -p -i.bak -e 's/gamma/'$beta'/' tmp;

If in doubt, it's often helpful to 'echo' your variables out to see exactly what they contain. I don't understand your final note, as the 'alpha' variable is not equal to 10\20\30 the way you have it originally assigned.

answered Mar 29, 2013 at 17:47

Jim Black

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3 Comments

user13107 Over a year ago

Hello, this works, but what if I have forward slashes in alpha? It gives another error then.

Jim Black Over a year ago

Did you mean to use the control characters from '\2' or '\3' or the sequence of a '\' followed by a '2' or '3'? If it is the former, then the backslashes in alpha will need to be escaped (backslashed) themselves. Like 'set alpha="10\\20\\30";'

user13107 Over a year ago

I found other alternative for forward slash case. instead of 's/gamma/'$beta'/' I use 's@gamma@'$beta'@'. This way it doesn't confuse forward slashes in $beta with substitution operator delimiters. Thanks for your help anyway.

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