Question

Most tar files extract into their own subfolder (because the people that write open source utilities are amazing people).

Some extract into my cwd, which clutters everything up. I know there’s a way to see what’s in the tar, but I want to write a bash script that essentially guarantees I won’t end up with 15 files extracted into my home folder.

Any pointers?

pseudo code:

if [listing of tar files] has any file that doesn't have a '/' in it:
    mkdir [tar filename without extension]
    tar xzvf [tar filename] into [the new folder]
else:
    tar xzvf [tar filename] into cwd

EDIT:

Both solutions are great, I chose the below solution because I was asking for a bash script, and it doesn’t rely on extra software.

However, on my own machine, I am using aunpack because it can handle many, many more formats.

I am using it with a shell script that downloads and unpacks all at once. Here is what I am using:

#!/bin/bash
wget -o temp.log --content-disposition $1
old=IFS
IFS='
'
r=`cat temp.log`
rm temp.log
for line in $r; do
    substring=$(expr "$line" : 'Saving to: `\(.*\)'\')
    if [ "$substring" != "" ]
    then
        aunpack $substring
        rm $substring
        IFS=$old
        exit
    fi
done
IFS=$old

Answer 1

You can use combination of tar options to achieve this:
tar option for listing is:

   -t, --list
          list the contents of an archive

tar option to extract into different directory is:

   -C, --directory DIR
          change to directory DIR

So in your script you can list the files & check if there are any files in the listing which do not have “/” and based on that output you can call tar with appropriate options.
Sample for your reference is as follows:

TAR_FILE=<some_tar_file_to_be_extracted>
# List the files in the .tgz file using tar -tf
# Look for all the entries w/o "/" in their names using grep -v 
# Count the number of such entries using wc -l, if the count is > 0, create directory
if [ `tar -tf ${TAR_FILE} |grep -v "/"|wc -l` -gt 0 ];then
   echo "Found file(s) which is(are) not in any directory"
   # Directory name will be the tar file name excluding everything after last "."
   # Thus "test.a.sh.tgz" will give a directory name "test.a.sh"
   DIR_NAME=${TAR_FILE%.*}
   echo "Extracting in ${DIR_NAME}"
   # Test if the directory exists, if not then create it
   [ -d ${DIR_NAME} ] || mkdir ${DIR_NAME}
   # Extract to the directory instead of cwd
   tar xzvf ${TAR_FILE} -C ${DIR_NAME}
else
   # Extract to cwd
   tar xzvf ${TAR_FILE}
fi

In some cases the tar file may contain different directories. If you find it a little annoying to look for different directories which are extracted by the same tar file then the script can be modified to create a new directory even if the listing contains different directories. The slightly advanced sample is as follows:

TAR_FILE=<some_tar_file_to_be_extracted>
# List the files in the .tgz file using tar -tf
# Look for only directory names using cut, 
# Current cut option used lists each files as different entry 
# Count the number unique directories, if the count is > 1, create directory
if [ `tar -tf ${TAR_FILE} |cut -d '/' -f 1|uniq|wc -l` -gt 1 ];then
   echo "Found file(s) which is(are) not in same directory"
   # Directory name will be the tar file name excluding everything after last "."
   # Thus "test.a.sh.tgz" will give a directory name "test.a.sh"
   DIR_NAME=${TAR_FILE%.*}
   echo "Extracting in ${DIR_NAME}"
   # Test if the directory exists, if not then create it
   # If directory exists prompt user to enter directory to extract to
   # It can be a new or existing directory
   if [ -d ${DIR_NAME} ];then
     echo "${DIR_NAME} exists. Enter (new/existing) directory to extract to"
     read NEW_DIR_NAME
     # Test if the user entered directory exists, if not then create it
     [ -d ${NEW_DIR_NAME} ] || mkdir ${NEW_DIR_NAME}
   else
     mkdir ${DIR_NAME}
   fi
   # Extract to the directory instead of cwd
   tar xzvf ${TAR_FILE} -C ${DIR_NAME}
else
   # Extract to cwd
   tar xzvf ${TAR_FILE}
fi

Hope this helps!