Perl command-line script and shell variables: How to quote?

Question

I have a shell script (csh) calling Perl like this:

set SHELL_VAR = "foo"
set RES = `perl -e 'my $perl_var = uc("$SHELL_VAR"); print "$perl_var\n"'`
echo $RES

I did not manage to use single or double quotes properly, no matter which combination I tried.

How do I properly mix variables in Perl and shell?

Both are starting with $. Double quotes use variable values, but returns

error perl_var: Undefined variable.

in shell. Enclosing a Perl script by single quotes led to an empty result. Escaping like \$perl_var does not succeed either.

See Csh Programming Considered Harmful, especially the section 4. QUOTING. — choroba
– choroba, Commented Jun 5, 2014 at 11:51

ikegami · Accepted Answer · 2014-06-05 14:13:05Z

2

You are trying to insert the value of a shell var into a Perl literal of a program that's in a command line. That's two levels of escaping! Instead, just pass it to Perl as an argument.

% set SHELL_VAR = "foo"
% set RES = `perl -e'print uc($ARGV[0])' "$SHELL_VAR"`
% echo "$RES"
FOO

Doh! It's not quite right.

csh% set SHELL_VAR = foo\"\'\(\ \ \ \$bar
csh% set RES = `perl -e'print uc($ARGV[0])' "$SHELL_VAR"`
csh% echo "$RES"
FOO"'( $BAR

I should get

FOO"'(   $BAR

In sh, I'd use RES="` ... `" aka "$( ... "), but I don't know the csh equivalent. If someone could fix the above so multiple spaces are printed, I'd appreciate it!

sh$ shell_var=foo\"\'\(\ \ \ \$bar
sh$ res="$( perl -e'print uc($ARGV[0])' "$shell_var" )"
sh$ echo "$res"
FOO"'(   $BAR

edited Jun 5, 2014 at 14:13

answered Jun 5, 2014 at 14:01

ikegami

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JRFerguson · Accepted Answer · 2014-06-05 12:01:49Z

1

You can push your SHELL_VAR into the environment and let Perl pull it from there:

#!/bin/csh
setenv SHELL_VAR "foo"
set RES = `perl -e 'my $perl_var = uc($ENV{SHELL_VAR}); print "$perl_var\n"'`
echo $RES

Note that the setenv command lacks the expicit '=' for assignment. The environmental variable is availab e to Perl from the %ENV hash with the variable name as its key.

answered Jun 5, 2014 at 12:01

JRFerguson

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Wernfried Domscheit · Accepted Answer · 2014-06-05 14:30:34Z

0

I found another solution, you can simply concatenate several expressions, i.e. you can write

set XYZ = "foo"`date`bar$HOST'gugus'

for example. This is a concatenation of

foo + `date` + bar + $HOST + gugus

Thus the following works:

set SHELL_VAR = "foo"
set RES = `perl -e 'my $perl_var = uc("'$SHELL_VAR'"); print "$perl_var\n"'`
echo $RES

answered Jun 5, 2014 at 14:30

Wernfried Domscheit

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