Bash script that can uncompress: tar, gzip, rar

Question

This code generally works exactly as it is supposed to. I'm learning bash I'm looking for some constructive help that could help me improve my work.

#!/bin/bash
usage()
{
 echo "Program for uncompressing tar, gzip, rar archives"
 echo "Allowed parametres: --help, --file, --input, --directory"
 echo "Examples:"
 echo "./uncompress.sh --file firstFile secondFile"
 echo "./uncompress.sh --input inputFile.txt"
 echo "./uncompress.sh --directory /home/"
}
uncompress_file()
{
 if [ -f 1ドル ]
 then
 temp1=`file 1ドル | cut -d: -f2 | grep tar`
 if [ "$temp1" != "" ]
 then
 echo "1ドル is a tar archive, uncompressing..."
 tar xf 1ドル > /dev/null
 fi
 temp1=`file 1ドル | cut -d: -f2 | grep RAR`
 if [ "$temp1" != "" ]
 then
 echo "1ドル is a rar archive, uncompressing..."
 unrar e 1ドル > /dev/null
 fi 
 temp1=`file 1ドル | cut -d: -f2 | grep gzip`
 if [ "$temp1" != "" ]
 then
 echo "1ドル is a gzip archive, uncompressing..."
 tar xzf 1ドル > /dev/null
 fi
 else
 echo "1ドル is not a valid file!"
 fi
}
uncompress_dir()
{
 for file in "1ドル"/*
 do
 if [ -f $file ]
 then
 uncompress_file $file
 fi
 if [ -d $file ]
 then
 uncompress_dir $file
 fi
 done
}
if [ "1ドル" = "--help" ]
 then
 usage
 exit
fi
if test $# -lt 2
 then echo "What about parametres?" 1>&2
 exit 1
fi
param=1ドル;
shift;
if [ "$param" = "--file" ]
 then
 while [ $# -ne 0 ]
 do
 uncompress_file 1ドル
 shift
 done
 exit
fi
if [ "$param" = "--input" ]
 then
 if [ -f 1ドル ]
 then
 while read line
 do
 uncompress_file $line
 done < 1ドル 
 else
 echo "1ドル is not a valid file"
 fi
 exit 
fi
if [ "$param" = "--directory" ]
 then
 if [ -d 1ドル ]
 then
 uncompress_dir 1ドル
 else
 echo "1ドル is not a valid directory"
 fi
 exit
fi
echo "wrong parametres!";

Answer 1

1. Don't use cut and grep, use parameter substitution and a case statement over the file extension to decide the file type (or use the file command if you want to be really clever, but I recommend the former actually)
2. Don't use [ "${foo}" != "" ], use [ -n "${foo}" ]
3. Don't mix test and [, just stick to [ unless you want to write code that looks autoconf generated
4. Quote all your variables, especially the ones containing filenames to account for spaces, e.g. tar xzf "1ドル" > /dev/null
5. Don't parse command line options yourself, use getopts (or getopt, in case you really, really want GNU-style options)
6. Improve your indentation

• Grzegorz Piwowarek: But file extension doesn't always match content of the file. How could You deal with it then? This is why I decided to extract desired information with file.
• Adrian Frühwirth: My thought pattern is that if a file has the "wrong" extension, in many cases you will want to know about that and not silently continue. The decompressor should error with an appropriate message anyway. Or you could e.g. implement a -g (for "guess") switch to use file instead of the file extension. But as I said, this is a matter of preference; if you want to use file, go ahead ;-) As an addition source of inspiration you might want to check the unpack function that Gentoo's portage uses here.

Answer 2

grep has a non-zero exit status if it finds no matches. So code like this

temp1=`file 1ドル | cut -d: -f2 | grep tar`
if [ "$temp1" != "" ]
then
 echo "1ドル is a tar archive, uncompressing..."
 tar xf 1ドル > /dev/null
fi

can be more succinctly written as

# -q causes grep to output nothing; we don't really care what it finds,
# just if it finds *something*
if file 1ドル | cut -d: -f2 | grep -q tar
then
 echo "1ドル is a tar archive, uncompressing..."
 tar xf "1ドル" > /dev/null
fi

---

Always quote parameter expansions, as I did above for the call to tar, just in case the value contains whitespace. It's almost never wrong to do so, and you never know when it might be absolutely necessary.