在bash shell脚本中检查目录的问题

Question

I am writing a batch-processing script bash that needs to first check to see if a folder exists to know whether or not to run a certain python script that will create and populate the folder. I have done similar things before that do fine with changing the directories and finding directories from a stored variable, but for some reason I am just missing something here.

Here is roughly how the script is working.

if [ -d "$net_output" ]
then
    echo "directory exists"
else
    echo "directory does not exist"
fi

when I run this script, I usually echo $net_output in the line before to see what it will evaluate to. When the script runs I get my else block of code saying "Directory does not exist", but when I then copy and paste the $net_output directory path that is echoed before into the shell terminal, it changes directories just fine, proving that the directory does in fact exist. I am using Ubuntu 12.04 on a Dell machine.

Thank you in advance for any help that someone can offer. Let me know what additional information I can provide.

Answer 1

The most common cases I've encountered when someone posts a problem like this are the following:

1. The variable contains literal quotes. Bash does not recursively parse quotes, it only parses the "outer" quotes given on the command line.

$ mkdir "/tmp/dir with spaces"
$ var='"/tmp/dir with spaces"'
$ echo "$var"
"/tmp/dir with spaces"
$ [ -d "/tmp/dir with spaces" ]; echo $?
0
$ [ -d "$var" ]; echo $?  # equivalent to [ -d '"/tmp/dir with spaces"' ]
1

2. The variable contains a relative path, and the current directory is not what you expected. Check that the value of echo "$PWD" outputs what you expected.

3. The variable was read from a file with dos line endings, CRLF (\\r\\n). Unix and unix-like systems use just LF (\\n) for line endings. If that's the case, the path will contain a CR (\\r) at the end. A CR at the end of a line will be "invisible" in a terminal. Check with printf '%q\\n' "$var" while debugging the script. See BashFAQ 52 on how to get rid of them.