Advanced Bash−Scripting Guide

#!/bin/bash
# grp.sh: Very crude reimplementation of 'grep'.
E_BADARGS=65
if [ −z "$1" ] # Check for argument to script.
then
echo "Usage: `basename $0` pattern"
exit $E_BADARGS
fi
echo
for file in * # Traverse all files in $PWD.
do
output=$(sed −n /"$1"/p $file) # Command substitution.
if [ ! −z "$output" ]
# What happens if "$output" is not quoted?
then
echo −n "$file: "
echo $output
fi
# sed −ne "/$1/s|^|${file}: |p" is equivalent to above.
echo
done
echo
exit 0
Advanced Bash−Scripting Guide
# Exercises:
# −−−−−−−−−
# 1) Add newlines to output, if more than one match in any given file.
# 2) Add features.
egrep is the same as grep −E. This uses a somewhat different, extended set of regular
expressions, which can make the search somewhat more flexible.
fgrep is the same as grep −F. It does a literal string search (no regular expressions),
which allegedly speeds things up a bit.
agrep extends the capabilities of grep to approximate matching. The search string
may differ by a specified number of characters from the resulting matches. This utility
is not part of the core Linux distribution.
To search compressed files, use zgrep, zegrep, or zfgrep. These also work on
non−compressed files, though slower than plain grep, egrep, fgrep. They are handy
for searching through a mixed set of files, some compressed, some not.
look
To search bzipped files, use bzgrep.
The command look works like grep, but does a lookup on a "dictionary", a sorted word list. By
default, look searches for a match in /usr/dict/words, but a different dictionary file may be
specified.
Chapter 12. External Filters, Programs and Commands 168