plugins: extract: add new preview-extract function

It is often desirable to inspect the contents of an archive before
unpacking it.  Add a new function, preview-extract, which does this.
preview-extract is a copy-paste of extract(), but the tar commands have
parameter 'x' replaced with 't' to print the pathes of any files in the
archive.

The non-tar lines have been commented out since I rarely use those and
don't know the equivalent parameters off hand.  Hopefully a kind soul
will add those in.

Signed-off-by: Michael Turquette <mturquette@deferred.io>

plugins/available/extract.plugin.bash

@@ -25,3 +25,29 @@ extract () {
 		echo "'$1' is not a valid file"
 	fi
 }
+
+extract-preview () {
+  if [ $# -ne 1 ]
+  then
+    echo "Error: No file specified."
+    return 1
+  fi
+	if [ -f $1 ] ; then
+		case $1 in
+			*.tar.bz2) tar tvjf $1   ;;
+			*.tar.gz)  tar tvzf $1   ;;
+			#*.bz2)     bunzip2 $1    ;;
+			#*.rar)     unrar x $1    ;;
+			#*.gz)      gunzip $1     ;;
+			*.tar)     tar tvf $1    ;;
+			*.tbz2)    tar tvjf $1   ;;
+			*.tgz)     tar tvzf $1   ;;
+			#*.zip)     unzip $1      ;;
+			#*.Z)       uncompress $1 ;;
+			#*.7z)      7z x $1       ;;
+			*)         echo "'$1' cannot be extracted via extract" ;;
+		esac
+	else
+		echo "'$1' is not a valid file"
+	fi
+}