BASH Cures Cancer

I am utilizing Google’s project hosting to host software which I create and feel is useful or want to keep track of. I called the project Brock’s Tools. The code that led me to create this project was a command I am calling prepend 1.1. (UPDATE: See this post on sponge as its a better general case tool.)

prepend, prepend’s files or standard input to a file. For example,  you have three files:

$ echo BROCK > a
$ echo DAVID > b
$ echo NOLAND > c

And you want to combine them into one file:

$ echo "My name is:" | prepend - a b c
$ cat c
My name is:
BROCK
DAVID
NOLAND

Or lets say you just want to append a file to itself:

$ cat a
BROCK
$ cat a >> a
cat: a: input file is output file

prepend does this:

$ prepend a
$ cat a
BROCK
BROCK

I come across the a situation where this would be useful quite often. Of course prepend’ing can be done in the shell:

$ { echo "My name is:"; cat a b c; } > tmp && mv -f tmp c
$ cat c
My name is:
BROCK
DAVID
NOLAND

However, that is unsafe and I have lost data that way. I perform this operation most often when dealing with XML. In this example, its trivial to open the file in an editor, but with a large file, its quite nasty to do so:

$ cat something.xml
<entry><blah/><more>stuff 1</more></entry>
<entry><blah/><more>stuff 2</more></entry>
<entry><blah/><more>stuff 3 </more></entry>
<entry><blah/><more>stuff 4</more></entry>
$ echo "</entries>" >> something.xml
$ cat something.xml
<entry><blah/><more>stuff 1</more></entry>
<entry><blah/><more>stuff 2</more></entry>
<entry><blah/><more>stuff 3 </more></entry>
<entry><blah/><more>stuff 4</more></entry>
</entries>
$ echo "<entries>" | prepend - something.xml
$ cat something.xml
<entries>
<entry><blah/><more>stuff 1</more></entry>
<entry><blah/><more>stuff 2</more></entry>
<entry><blah/><more>stuff 3 </more></entry>
<entry><blah/><more>stuff 4</more></entry>
</entries>