Searching Files on UNIX

Test

On MPE you can display filesusing the rint command, Fcopy, Magnet,or Qedit (with patternmatch searches). On HP-UXyou can display files using cat and even better usingmore (and string search using the slash "/" command), andQedit (including searches of $Include files, and so on),but if you really want to search for patterns of textlike a UNIX guru, grep is the tool for you.Text version.

cat report.c	{prints file on stdout, no pauses}
cat -v -e -t dump	{show non-printing characters too}
cat >newfile	{reads from stdin, writes to 'newfile'}
cat rpt1.c inp.c test.s >newfile	{combine 3 files into 1}
more report.c	{space for next page, q to quit}
ps -a | more	{page through the full output of ps}
grep smug *.txt	{search *.txt files for 'smug'}

MPE users will take a while to remember thatmore, like most UNIX tools,responds to a Return by printing the next line,not the next screen. Use the Spacebar to print the nextpage.  Type "q" to quit.To scan ahead to find a string pattern, type "/" and entera regular expression to match.For further help, type "h".
Searching Files Using UNIX grepThe grep program is a standardUNIXutility that searches through a set of files for an arbitrary textpattern, specified through aregular expression.Also check the man pages as wellfor egrep and fgrep. TheMPEequivalents areMPEXandMagnet, both third-party products.By default, grep is case-sensitive (use -i to ignore case).By default, grep ignores the context of a string (use -w tomatch words only).By default, grep shows the lines that match (use -v to showthose that don't match).Text version.

% grep BOB tmpfile	{search 'tmpfile' for 'BOB' anywhere in a line}
% grep -i -w blkptr *	{search files in CWD for word blkptr, any case}
% grep run[- ]time *.txt	{find 'run time' or 'run-time' in all txt files}
% who | grep root	{pipe who to grep, look for root}

Understanding Regular ExpressionsRegular Expressions are a feature of UNIX.They describe a pattern to match, a sequence of characters,not words, within a line of text.Here is a quick summary of the special characters usedin the grep tool and their meaning:Text version.

^ (Caret)	=	match expression at the start of a line, as in ^A.
$ (Question)	=	match expression at the end of a line, as in A$.
\ (Back Slash)	=	turn off the special meaning of the next character, as in \^.
[ ] (Brackets)	=	match any one of the enclosed characters, as in [aeiou].Use Hyphen "-" for a range, as in [0-9].
[^ ]	=	match any one character except those enclosed in [ ], as in [^0-9].
. (Period)	=	match a single character of any value, except end of line.
* (Asterisk)	=	match zero or more of the preceding character or expression.
\{x,y\}	=	match x to y occurrences of the preceding.
\{x\}	=	match exactly x occurrences of the preceding.
\{x,\}	=	match x or more occurrences of the preceding.

As an MPE user, you mayfind regular expressions difficult to use at first.Please persevere, because they are used in manyUNIX tools, from more to perl.Unfortunately, some tools use simple regular expressions and others use extendedregular expressions and some extended features have been mergedinto simple tools, so that it looks as if every tool has its ownsyntax. Not only that, regular expressions use thesame characters as shell wildcarding,but they are not used in exactly the same way.What do you expect of an operating system built by graduate students?
Since you usually type regular expressions withinshell commands, it is good practice to enclose the regularexpression in single quotes (') to stop the shell from expandingit before passing the argument to your search tool.Here are some examples using grep:
Text version.

grep smug files	{search files for lines with 'smug'}
grep '^smug' files	{'smug' at the start of a line}
grep 'smug$' files	{'smug' at the end of a line}
grep '^smug$' files	{lines containing only 'smug'}
grep '\^s' files	{lines starting with '^s', "\" escapes the ^}
grep '[Ss]mug' files	{search for 'Smug' or 'smug'}
grep 'B[oO][bB]' files	{search for BOB, Bob, BOb or BoB }
grep '^$' files	{search for blank lines}
grep '[0-9][0-9]' file	{search for pairs of numeric digits}

Back Slash "\" is used to escape the nextsymbol, for example, turn off the special meaning that it has.To look for a Caret "^" at the start of a line, theexpression is ^\^.Period "." matches any single character. So b.b willmatch "bob", "bib", "b-b", etc.Asterisk "*" does not mean the same thing in regular expressionsas in wildcarding; it is a modifier that applies to thepreceding single character, or expression such as [0-9].An asterisk matches zero or more of what precedes it.Thus [A-Z]* matches any number of upper-case letters,including none, while [A-Z][A-Z]* matches oneor more upper-case letters.
The vi editor uses \< \> to match charactersat the beginning and/or end of a word boundary.A word boundary is either the edge of the line or any characterexcept a letter, digit or underscore "_".To look for if, but skip stiff, theexpression is \<if\>.For thesame logic in grep, invoke it with the -w option.And remember thatregular expressions are case-sensitive.  If you don'tcare about the case, the expression to match "if" would be[Ii][Ff],where the characters in square brackets define a characterset from which the pattern must match one character. Alternatively, youcould also invoke grep with the -i option to ignore case.
Here are a few more examples of grep to show you whatcan be done:
Text version.

grep '^From: ' /usr/mail/$USER	{list your mail}
grep '[a-zA-Z]'	{any line with at least one letter}
grep '[^a-zA-Z0-9]	{anything not a letter or number}
grep '[0-9]\{3\}-[0-9]\{4\}'	{999-9999, like phone numbers}
grep '^.$'	{lines with exactly one character}
grep '"smug"'	{'smug' within double quotes}
grep '"*smug"*'	{'smug', with or without quotes}
grep '^\.'	{any line that starts with a Period "."}
grep '^\.[a-z][a-z]'	{line start with "." and 2 lc letters}

http://www.robelle.com/smugbook/regexpr.html