bash Cookbook

Keeping Your Data with Your Script

Problem

You need input to your script, but don’t want a separate file.

Solution

Use a here-document, with the << characters, redirecting the text from the command line rather than from a file. When put into a shell script, the script file then contains the data along with the script.

Here’s an example of a shell script in a file we call ext:

$ cat ext
#
#
here is a "here" document
# grep $1 <<EOF
mike x.123
joe  x.234
sue  x.555
pete x.818
sara x.822
bill x.919
EOF
$

It can be used as a shell script for simple phone number lookups:

$ ext bill
bill x.919
$

or:

$ ext 555
sue x.555
$

Discussion

The grep command looks for occurrences of the first argument in the files that are named, or if no files are named it looks to standard input.

A typical use of grep is something like this:

$ grep somestring file.txt

or:

$ grep myvar *.c

In our ext script we’ve parameterized the grep by making the string that we’re searching for be the parameter of our shell script ($1). Whereas we often think of grep as searching for a fixed string through various different files, here we are going to vary what we search for, but search through the same data every time.

We could have put our phone numbers in a file, say phonenumbers.txt, and then used that filename on the line that invokes the grep command:

grep $1 phonenumbers.txt

However, that requires two separate files (our script and our datafile) and raises the question of where to put them and how to keep them together.

So rather than supplying ...