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Jovin Miranda
Asked: 2018-08-29 10:55:22 +0800 CST

Error while executing read prompt in csh and converting to multiline alias

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Hey everyone i have this issue where i have a sample program in csh (i know its not the best language to use for scripting but i dont have an option here) its as foll:

#!/bin/csh    
echo 'please enter values' 
read a 
read -e b
echo "My values are $a and $b"

As you might see my second read is going to take a file input. This is needed as my actual program will have that; now what i want to do is to convert this to alias however when i execute the above script i get the foll. output

please enter values
read: Command not found
read: Command not found
a: Undefined variable

How can i fix this and also i want to convert this all 4 lines into a multiline alias. I have written single line alias in the past with no issues but not sure about multiline. if someone can help out i'll be really grateful

scripts alias csh tcsh

1 Answers

  1. Best Answer

    As you have discovered, the C shell does not have a built-in read function similar to that of Bourne-type shells.

    I am not proficient in csh synatax but as far as I know, the nearest equivalent is to use the special variable $< . From man csh:

           $<      Substitutes a line from the standard input, with no further
               interpretation.  It can be used to read from the keyboard
               in a shell script.

    e.g.

    $ cat myscript.csh
#!/bin/csh

echo 'please enter values'
set a = $<
set b = $<
echo "My values are $a and $b"

    which gives

    $ ./myscript.csh
please enter values
123
abc
My values are 123 and abc

    Note that there are implementation-dependent differences in how assignments from $< handles multi-word input - in particular, the Tenex tcsh does not quote input by default, instead requiring $<:q to get the same behavior as BSD csh. Also there is (as far as I know) no built-in readline editing support equivalent to the bash shell's read -e.

    As far as multi-line aliases are concerned, they do seem to work:

    % alias jo '\
echo "please enter values "\
set a = $< \
set b = $< \
echo "My values are $a and $b"'
%
% alias
jo
echo "please enter values "
set a = $<
set b = $<
echo "My values are $a and $b"

    Testing it

    % jo
% please enter values
123
foo bar
My values are 123 and foo bar
%

    however it's not a feature that I would recommend relying on.

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