Strange error checking if directory exists with Bash script

Question

Here's a bash script I'm working on:

dir="~/path/to/$1/folder"

if [ -d "$dir" ]; then
    # do some stuff
else
    echo "Directory $dir doesn't exist";
    exit 1
fi

and when I run it from the terminal:

> ./myscript.sh 123
Directory ~/path/to/123/folder doesn't exist

But that folder clearly does exist. This works normally:

> ls ~/path/to/123/folder

What am I doing wrong?

Adam Rosenfield · Accepted Answer · 2009-06-10 00:29:02Z

5

The problem is that bash performs tilde expansion before shell parameter substitution, so after it substitutes ~/path/to/folder for $dir, it doesn't try to expand the ~, so it looks for a directory literally named with a tilde in it, which of course doesn't exist. See section 3.5 of the bash manual for a more detailed explanation on bash's expansions.

edited Jun 10, 2009 at 0:29

answered Jun 10, 2009 at 0:09

Adam Rosenfield

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Joakim Elofsson · Accepted Answer · 2009-06-10 00:09:12Z

1

try:

dir="$HOME/path/to/$1/folder"

answered Jun 10, 2009 at 0:09

Joakim Elofsson

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1 Comment

lhunath Over a year ago

Just because Joakim provided no explanation at all: You had quoted the ~. ~ only expands in bash during tilde expansion, but anything that you quote, you disable the special meaning of, so the tilde (~) no longer meant "expands to the home directory of the current user". It just meant: "the directory in the current directory called ~". Which didn't exist, hence the error.

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