Idea Machine PSEUDO-RANDOM THOUGHTS OF A WEB DEVELOPER AND DESIGNER

When coding in bash, files and directories with spaces (like GPS 1.3) can be particularly tricky. I bumped into this problem as I was trying to make the package for Gimp Paint Studio for Arch User Repository. Handling white space in your shell script is not so intuitive, and it differs a bit from how you do it on the command line, but I’ve finally got it.

First of all, here’s what happens to a string when you write it in your bash script.

Let’s prepare the working environment. In your home directory, create a directory called Directory with spaces. Inside that directory, touch a few files. I named my files file1, file2, and file3.

Create a shell script and save the following content in there:

#!/bin/bash

echo "First try"
ls ~/Directory with spaces

echo "Second try"
ls ~/Directory\ with\ spaces

echo "Third try"
ls "~/Directory with spaces"

echo "Fourth try"
ls "~/Directory\ with\ spaces"

After executing the script, you will see the following output:

First try
ls: cannot access /home/suzana/Directory: No such file or ...
ls: cannot access with: No such file or directory
ls: cannot access spaces: No such file or directory
Second try
file1  file2  file3
Third try
ls: cannot access ~/Directory with spaces: No such file or ...
Fourth try
ls: cannot access ~/Directory\ with\ spaces: No such file or ...

Clearly, only one solution works. And the winner is: second solution. In the second solution, we only used escape character to mark the spaces.

Ok, let’s modify our script a little.

!/bin/bash

VARIABLE="Directory with spaces"

echo "First try"
ls $VARIABLE

echo "Second try"
ls "$VARIABLE"

echo "Third try"
ls ${VARIABLE// /\\ /}

This time we’ve used a variable. (Don’t add spaces around the assignment operator =.) And the results are:

First try
ls: cannot access Directory: No such file or directory
ls: cannot access with: No such file or directory
ls: cannot access spaces: No such file or directory
Second try
file1  file2  file3
Third try
ls: cannot access Directory\: No such file or directory
ls: cannot access /with\: No such file or directory
ls: cannot access /spaces: No such file or directory

Again the second solution works, which is quoting the variable. How about something more exotic this time? How about our own version of ls?

!/bin/bash

for file in ~/Directory\ with\ spaces/*
do
    echo "Let's go"
    echo "$file"
    echo $file
    echo ${file// /\\ }
done

The results are:

Let's go
/home/suzana/Directory with spaces/file1
/home/suzana/Directory with spaces/file1
/home/suzana/Directory\ with\ spaces/file1
...

First thing first. The for loop (3rd line) uses the same method as the first example. I’ve tried other methods, but this one was the only one that works Also, I’ve included three echo lines to demonstrate how different ways of using the variable work. You have to note that the first and second echo commands yield similar results, but we already know that when passing file paths that contain spaces to commands, only the quoted variable works.

The last echo line is a very cool trick I’ve learned. When substituting variable using the { }, you can also do a quick string substitution. The syntax is:

${varname/string/replace} # replace first 'string' with 'replace'
${varname//string/replace} # replace all 'string' with 'replace'

I hope this will come in handy sometimes. Happy hacking!

Sometimes you need to get the current working directory for your script. There is a nice little function that gets you just that, and it’s called getcwd. Here’s a small example:

Create a file called getcwd.py and put the following in there:

#!/bin/env python
import os
print os.getcwd()

Now you run it like this:

$ python getcwd.py 
/home/foxbunny
$ cd Video
$ python ~/getcwd.py 
/mnt/storage/Video 

You have to note that the working directory is the directory from which you run the script, not where the script is physically located.