Tilde Expansion in Environment Variable

tilde expansion in environment variable

use

SOME_PATH=~/path/to/path/

if you path have spaces, quote it

SOME_PATH=~/"path with spaces"

tilde expansion when evaluating $PATH

No, this is not portable. If your operating system's execl call doesn't perform this expansion, programs that aren't bash will fail to find executables within the given directory.

Note that if you didn't quote the expansion, this would be safe:

PATH=$PATH:~/tempdir   # this is safe -- expansion happens before assignment
PATH="$PATH:~/tempdir" # this is not -- readers are required to expand

While it's generally a best practice to quote all shell expansions, this isn't necessary for assignments, which implicitly prevent string-splitting and glob expansion behaviors.

Tilde not expanded when quoting on the right hand side of a Bash variable assignment

Quotation marks prevent expansion of ~. Replace ~ with $HOME or use dirName=~/"test_$x".

From the manual's explanation of tilde expansion:

Each variable assignment is checked for unquoted tilde-prefixes immediately following a : or the first =. In these cases, tilde expansion is
also performed.

Can I use environment variables or tilde in module.modulemap?

No, the modulemap syntax does not expand tildes or environment variables. It ultimately just expects to stat the path you gave it, and if no file's there, it'll gripe.

• Here's where the header file lookup is kicked off, during lexing of the module map file.
• It ultimately passes the path to the SourceManager's FileManager to produce a File object, as here for a header in a framework's Headers/ public header folder.
• getFile ultimately ends up calling out to getStatValue, which does a cache lookup.
• The FileSystemStatCache::get eventually grounds out in LLVM's filesystem abstraction, where it calls sys::fs::status, which is documented to act like POSIX stat.
• POSIX stat works with paths as-is, no tilde or environment variable expansion - the common availability of those is due to the shell helping you out, not something that happens automatically most of the time at the system level.

However, it's standard to use relative paths in module maps. The lexer respects this, and all the module map docs demonstrate this. In the common case where your module map file is colocated with your library and installed alongside it, this should suffice to properly resolve the paths.

How to manually expand a special variable (ex: ~ tilde) in bash

Due to the nature of StackOverflow, I can't just make this answer unaccepted, but in the intervening 5 years since I posted this there have been far better answers than my admittedly rudimentary and pretty bad answer (I was young, don't kill me).

The other solutions in this thread are safer and better solutions. Preferably, I'd go with either of these two:

• Charle's Duffy's solution
• Håkon Hægland's solution

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Original answer for historic purposes (but please don't use this)

If I'm not mistaken, "~" will not be expanded by a bash script in that manner because it is treated as a literal string "~". You can force expansion via eval like this.

#!/bin/bash

homedir=~
eval homedir=$homedir
echo $homedir # prints home path

Alternatively, just use ${HOME} if you want the user's home directory.

Why use $HOME over ~ (tilde) in a shell script?

Tilde expansion doesn't work in some situations, like in the middle of strings like /foo/bar:~/baz

Tilde (~/) not working on if then statement in Shell script

Double quotes (really, any quotes) prevent ~ from being expanded. Use instead:

checkfile=~/mysql_backup/"$file"

...or, even better, use $HOME in all scripts, and consider ~ to be a facility for interactive/human use only.

How to expand tilde (~) in path

Original answer

Try this:

eval directory="$directory"

Since nothing can interpret the special shell characters better than the shell itself, it is a good idea to ask the shell to evaluate the expression for us. And eval is just the command that evaluates shell expressions.

Alternative #1: program in C

However, eval is unsafe, as it has been mentioned many times, - it may execute malicious code, or cause unwanted effects. Then, for a POSIX environment, you can write a simple program in C:

tildeexp.c

#include <stdio.h>
#include <stdlib.h>
#include <wordexp.h>

int
main(int argc, char **argv)
{
  wordexp_t p;
  int rc;

  rc = wordexp(argv[1], &p, 0);
  if (rc) {
    fprintf(stderr, "Failed to expand %s: %d\n",
        argv[1], rc);
  } else {
    printf("%s\n", p.we_wordc ? p.we_wordv[0] : "");
  }
  wordfree(&p);

  return (rc ? 1 : 0);
}

Compiling

gcc -Wall -g -O2 -o tildeexp tildeexp.c

Usage

directory=$(/path/to/tildeexp "$directory")
if [ $? -eq 0 ]; then
  # success
else
  # failed to expand
fi

Alternative #2: Perl's glob

directory="${directory//$"'"/$"\\'"}"
directory=$(perl -e "print glob('$directory')")

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