Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
grep −c txt *.sgml
# (number of occurrences of "txt" in "*.sgml" files)
# grep −cz .
# ^ dot
# means count (−c) zero−separated (−z) items matching "."
# that is, non−empty ones (containing at least 1 character).
#
printf 'a b\nc d\n\n\n\n\n\000\n\000e\000\000\nf' | grep −cz . # 4
printf 'a b\nc d\n\n\n\n\n\000\n\000e\000\000\nf' | grep −cz '$' # 5
printf 'a b\nc d\n\n\n\n\n\000\n\000e\000\000\nf' | grep −cz '^' # 5
#
printf 'a b\nc d\n\n\n\n\n\000\n\000e\000\000\nf' | grep −c '$' # 9
# By default, newline chars (\n) separate items to match.
# Note that the −z option is GNU "grep" specific.
# Thanks, S.C.
When invoked with more than one target file given, grep specifies which file contains matches.
bash$ grep Linux osinfo.txt misc.txt
osinfo.txt:This is a file containing information about Linux.
osinfo.txt:The GPL governs the distribution of the Linux operating system.
misc.txt:The Linux operating system is steadily gaining in popularity.
To force grep to show the filename when searching only one target file, simply give
/dev/null as the second file.
bash$ grep Linux osinfo.txt /dev/null
osinfo.txt:This is a file containing information about Linux.
osinfo.txt:The GPL governs the distribution of the Linux operating system.
If there is a successful match, grep returns an exit status of 0, which makes it useful in a condition test
in a script, especially in combination with the −q option to suppress output.
SUCCESS=0
word=Linux
filename=data.file
grep −q "$word" "$filename"
# if grep lookup succeeds
# The "−q" option causes nothing to echo to stdout.
if [ $? −eq $SUCCESS ]
then
echo "$word found in $filename"
else
echo "$word not found in $filename"
fi
Example 30−6 demonstrates how to use grep to search for a word pattern in a system logfile.
Example 12−12. Emulating "grep" in a script
Chapter 12. External Filters, Programs and Commands 167