Shell Complex Commands - Part II

grep -
To force grep to show the filename when searching only one target file, simply give /dev/null as the second file.
grep Linux osinfo.txt /dev/null

egrep -- extended grep --
Is the same as grep -E. This uses a somewhat different, extended set of Regular Expressions, which can make the search a bit more flexible. It also allows the boolean | (or) operator.
For example,
bash $ egrep 'matches|Matches' file.txt
Line 1 matches.
Line 3 Matches.
Line 4 contains matches, but also Matches

look
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.
Example,

#!/bin/bash
# lookup: Does a dictionary lookup on each word in a data file.
file=words.data # Data file from which to read words to test.
echo
while [ "$word" != end ] # Last word in data file.
do # ^^^
read word # From data file, because of redirection at end of loop.
look $word > /dev/null # Don't want to display lines in dictionary file.
lookup=$? # Exit status of 'look' command.
if [ "$lookup" -eq 0 ]
then
echo "\"$word\" is valid."
else
echo "\"$word\" is invalid."
fi
done <"$file" # Redirects stdin to $file, so "reads" come from there.
echo