How to scape shell variable with spaces within AWK script - bash

Question

I have the path of "file1 Nov 2018.txt" stored in variable "var". Then I use this shell variable inside the awk script
to generate another script (this is a small example). The issue is the path and the filename have spaces and even I put the variable between double quotes ""
and within awk I put between single quotes '' is not working either. I get the error "No such file or directory"
How to handle this path that has spaces?
The script is like this:
var="/mydrive/d/data 2018/Documents Nov/file1 Nov 2018.txt"
z=$(awk -v a="$var" 'BEGIN{str = "cat " 'a' ; print str}')
eval "$z"
I get these errors:
$ eval "$z"
cat: /mydrive/d/data: No such file or directory
cat: 2018/Documents: No such file or directory
cat: Nov/file1: No such file or directory
cat: Nov: No such file or directory
cat: 2018.txt: No such file or directory
Thanks for any help.

Answer 1

The single-quote escape sequence comes in handy here. Note that 047 is the value in octal for the ASCII ' character, and awk allows you to use \nnn within a string to include any character using its octal value.
$ cat 'foo bar.txt'
a b c
1 2 3
$ var="foo bar.txt"
$ echo "$var"
foo bar.txt
$ z=$(awk -v a="$var" 'BEGIN{print "cat \047" a "\047"}')
$ eval "$z"
a b c
1 2 3
Maybe it's a bit nicer with printf:
$ awk -v a="$var" 'BEGIN{ printf "cat \047%s\047\n", a }'
cat 'foo bar.txt'
The problem is coming from the fact that the single quote has special meaning to the shell, so it's not surprising that there's a clash when single quotes are also being used in your awk program, when that program is on the command line.
This can be avoided by putting the awk program in its own file:
$ cat a.awk
BEGIN { printf "cat '%s'\n", a }
$ awk -v a="$var" -f a.awk
cat 'foo bar.txt'

Answer 2

remove the single quotes around a and add escaped double quotes instead.
$ echo success > "a b"
$ var="a b"; z=$(awk -v a="$var" 'BEGIN{print "cat \"" a "\""}');
$ eval "${z}"
success
however, most likely you're doing some task unnecessarily complex.

Answer 3

$ cat > path\ to/test
foo
$ z=$(awk -v a="$var" 'BEGIN{gsub(/ /,"\\ ",a); str = "cat " a ; print str}')
$ echo "$z"
cat path\ to/test
$ eval "$z"
foo
The key (in this solution) being: gsub(/ /,"\\ ",a) ie. escaping the spaces with a \ (\\ due to awk).

Answer 4

With bash's printf %q "$var" you can correctly escape any string for later use in eval - even linebreaks will be handled correctly. However, the resulting string may contain special symbols like \ that could be interpreted by awk when assigning variables with awk -v var="$var". Therefore, better pass the variable via stdin:
path='/path/with spaces/and/special/symbols/like/*/?/\/...'
cmd=$(printf %q "$path" | awk '{print "cat "$0}')
eval "$cmd"
In this example the generated command $cmd is
cat /path/with\ spaces/and/special/symbols/like/\*/\?/\\/...