Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
# /var/log/messages must have world read permission for this to work.
echo "$filename contains tail end of system log."
exit 0
grep
See also Example 12−4, Example 12−30 and Example 30−6.
A multi−purpose file search tool that uses regular expressions. It was originally a command/filter in
the venerable ed line editor, g/re/p, that is, global − regular expression − print.
grep pattern [file...]
Search the target file(s) for occurrences of pattern, where pattern may be literal text or a
regular expression.
bash$ grep '[rst]ystem.$' osinfo.txt
The GPL governs the distribution of the Linux operating system.
If no target file(s) specified, grep works as a filter on stdout, as in a pipe.
bash$ ps ax | grep clock
765 tty1 S 0:00 xclock
901 pts/1 S 0:00 grep clock
The −i option causes a case−insensitive search.
The −w option matches only whole words.
The −l option lists only the files in which matches were found, but not the matching lines.
The −r (recursive) option searches files in the current working directory and all subdirectories below
it.
The −n option lists the matching lines, together with line numbers.
bash$ grep −n Linux osinfo.txt
2:This is a file containing information about Linux.
6:The GPL governs the distribution of the Linux operating system.
The −v (or −−invert−match) option filters out matches.
grep pattern1 *.txt | grep −v pattern2
# Matches all lines in "*.txt" files containing "pattern1",
# but ***not*** "pattern2".
The −c (−−count) option gives a numerical count of matches, rather than actually listing the
matches.
Chapter 12. External Filters, Programs and Commands 166