#!/bin/bash
#
# This is a further example of how you can make a program that acts as a
# typical filter program, BUT will also decompress any *.gz files that are
# passed as arguments. This is useful for creating log-processing scripts.
#
# Cameron Kerr <ckerr@cs.otago.ac.nz>
# 19 March 2008
#
# Released under the Public Domain
#
# Note: Normally, you might just use something like the following, where
#       filter-script is the script that calls a particular filter-prog:
#         filter-prog "$@" | ...
#       which will work for the following examples
#         ... | filter-script | ...
#         filter-script < file
#         filter-script file ...
#       but will not work correctly for
#         filter-script file file2.gz ...
#
# Note2: I'm using cat here, which is generally unoptimal, but in this case
#       its worth it to make the function get its input from stdin if needed.
#
# Note3: I'm using 'file' to determine the type of file we're dealing with,
#       rather than its extension.
#
# Note4: I've only really tested this on Mac OS X, and a little bit on Linux.
#       Please report bugs.
#
# Note5: You can also specify - as an input file (this is common practice).
#       And like other programs (eg. cat) you can specify it multiple times.

# Pass this function "$@", which should be all the files (or none) that the
# user wishes to get the input from.
#
get-lines() {
    if [ $# -eq 0 ]; then
        cat
    else
        for file in "$@"; do
            if [ -r "$file" ]; then
                magic=$(file -b -- "$file")
                case "$magic" in
                    'gzip compressed data'*)
                        gzip -dc -- "$file"
                        ;;
                    'bzip2 compressed data'*)
                        bzip2 -dc -- "$file"
                        ;;
                    "compress'd data"*)
                        uncompress -dc -- "$file"
                        ;;
                    *)
                        cat -- "$file"
                        ;;
                esac
            elif [ x"$file" = x- ]; then  # [ - = - ] is bad, hence x
                cat
            else
                echo "$file: No such file or directory, or no permission to read." >&2
            fi
        done
    fi
}

# Testing
get-lines "$@" | wc -l