[Bash] Manipulate JAR (Java ARchive) file with extension .jar

manipulate-jar.bash

#!/usr/bin/env bash

usage() {
  cat << EOF
usage: `basename "$0"` jar_name [file_name]

See content of archive jar, then content of a file if precised.
EOF
  exit 1
}

if [ $# -eq 0 -o $# -gt 2 ]; then 
  usage
fi

jar_name="$1"
file_name="$2"

# see file system in a jar file
jar tfv "$jar_name"

# see content of <file_name> in <jar_name>
if [ -n "$file_name" ]; then
  unzip -p "$jar_name" "$file_name"
fi