Invoking a command line with spaces from a variable in a Bash script [duplicate]

Answer 1

Calling exec on your string, you actually end up executing cmake with the following arguments:

1: .
2: -G
3: "Unix
4: Makefiles"

exec itself doesn't interpret quotes, but just spaces, and passes the arguments this way to the execve system call. You need to let Bash interpret the quotes by using a built-in like eval.

Answer 2

Use eval to tell the shell to parse the command-line anew:

c="cmake . -G \"Unix Makefiles\""
eval "$c"

Alternatively, I like using arrays to avoid the unnecessary backslashes and eval:

# Store command in 4-element array: ["cmake", ".", "-G", "Unix Makefiles"].
# No backslash escapes needed.
c=(cmake . -G "Unix Makefiles")

# Ugly syntax for expanding out each element of an array, with all the spaces and
# quoting preserved to ensure that "Unix Makefiles" remains a single word.
"${c[@]}"

Answer 3

You may also use ... | xargs bash -c '...' to reparse a string as command line arguments. (Using xargs may, however, not be the ideal solution for multiple platforms.)

# Example: find file names with a space
c=". -maxdepth 3 -name \"* *\""
printf '%s' "$c" | xargs bash -c 'set -xv; find "$@"' arg0 2>&1| less

Another option would be to use a shebang helper like shebang.c!

Answer 4

The Bash FAQ to the rescue: The quotes are syntactical (meaning the quotes are not part of the name), so you should get the expected result with this:

if test [.... this is Unix ...]
    target="Unix Makefiles"
else
    target="MSYS Makefiles"
fi
cmake . -G "$target"

PS: eval is evil

Answer 5

It is best not to use eval unnecessarily. Try not to put the command inside a variable. You can put the options as a variable though:

if [ ... ]
  string="Unix makefiles"
else
  string="MSYS Makefiles"
else
  string="...."
fi
cmake -G "$string" # Just call the command normally