O’Reilly Books Latest LAMP Titles: mod_perl Pocket Reference SQL in a Nutshell Network Printing Books by topic: Linux Open Source Security System and Network Administration Unix Web and Internet O’Reilly Network Technologies: ONJava.com ONLamp.com openp2p.com Perl.com XML.com Apache BSD Java Javascript and CSS Linux Mac Mozilla .NET P2P Perl Policy PHP Python Web Services Wireless
Sponsored by: Search | Newsletter | Conference | Tech Jobs O’Reilly’s Emerging Technology Conference: May 13-16, 2002 Articles Linux Apache MySQL Perl PHP Python BSD Essentials What is LAMP? The Best of ONLamp.com aboutSQL Big Scary Daemons FreeBSD Basics HTTP Wrangler Linux in the Enterprise Linux Network Administration The Linux Professional Perl P5P Digest Archive PHP Admin Basics PHP Phanatics Python_News Security Alerts Alphabetical Directory of Linux Commands This directory of Linux commands is from Linux in a Nutshell, 3rd Edition. Click on any of the 379 commands below to get a description and list of available options. All links in the command summaries point to the online version of the book on Safari Tech Books Online. Buy it now Read it online false A null command that returns an unsuccessful (nonzero) exit status. Normally used in bash scripts. See also true. Return to: Alphabetical Directory of Linux Commands Sponsored by:
Print the number of lowercase letters at the beginning of p: expr $p : ‘[a-z]*’ Result is 7 Match the lowercase letters at the beginning of p: expr $p : ‘([a-z]*)’ Result is “version” Truncate $x if it contains five or more characters; if not, just print $x. (Logical OR uses the second argument when the first one is 0 or null; i.e., when the match fails.) expr $x : ‘(…..)’ | $x In a shell script, rename files to their first five letters: mv $x expr $x : ‘(…..)’ | $x (To avoid overwriting files with similar names, use mv -i.) Return to: Alphabetical Directory of Linux Commands Copyright 2000-2002 O’Reilly & Associates, Inc. All Rights Reserved. All trademarks and registered trademarks appearing on the O’Reilly Network are the property of their respective owners. For problems or assistance with this site, email help@oreillynet.com
XML length string Return the length of string. match string regex Same as string : regex. quote token Treat token as a string, even if it would normally be a keyword or an operator. substr string start length Return a section of string, beginning with start, with a maximum length of length characters. Return null when given a negative or nonnumeric start or length. Examples Division happens first; result is 10: expr 5 + 10 / 2 Addition happens first; result is 7 (truncated from 7.5): expr ( 5 + 10 ) / 2 Add 1 to variable i. This is how variables are incremented in shell scripts: i= expr $i + 1 Print 1 (true) if variable a is the string “hello”: expr $a = hello Print 1 (true) if b plus 5 equals 10 or more: expr $b + 5 >= 10 Find the 5th, 6th, and 7th letters of the word character: expr substr character 5 3 In the examples that follow, variable p is the string “version.100″. This command prints the number of characters in p: expr $p : ‘.*’ Result is 11 Match all characters and print them: expr $p : ‘(.*)’ Result is “version.100″
O’Reilly Books Latest LAMP Titles: mod_perl Pocket Reference SQL in a Nutshell Network Printing Books by topic: Linux Open Source Security System and Network Administration Unix Web and Internet O’Reilly Network Technologies: ONJava.com ONLamp.com openp2p.com Perl.com XML.com Apache BSD Java Javascript and CSS Linux Mac Mozilla .NET P2P Perl Policy PHP Python Web Services Wireless Use these to compare two arguments. Arguments can also be words, in which case comparisons are defined by the locale. If the comparison statement is true, the result is 1; if false, the result is 0. Symbols > and < must be escaped. =, == Are the arguments equal? != Are the arguments different? > Is arg1 greater than arg2? >= Is arg1 greater than or equal to arg2? < Is arg1 less than arg2? <= Is arg1 less than or equal to arg2? Logical operators Use these to compare two arguments. Depending on the values, the result can be arg1 (or some portion of it), arg2, or 0. Symbols | and & must be escaped. | Logical OR; if arg1 has a nonzero (and nonnull) value, the result is arg1; otherwise, the result is arg2. & Logical AND; if both arg1 and arg2 have a nonzero (and nonnull) value, the result is arg1; otherwise, the result is 0. : Like grep; arg2 is a pattern to search for in arg1. arg2 must be a regular expression. If part of the arg2 pattern is enclosed in ( ), the result is the portion of arg1 that matches; otherwise, the result is simply the number of characters that match. By default, a pattern match always applies to the beginning of the first argument (the search string implicitly begins with a ^). Start the search string with .* to match other parts of the string. Keywords index string character-list Return the first position in string that matches the first possible character in character-list. Continue through character-list until a match is found, or return 0.
Sponsored by: Search | Newsletter | Conference | Tech Jobs O’Reilly’s Emerging Technology Conference: May 13-16, 2002 Articles Linux Apache MySQL Perl PHP Python BSD Essentials What is LAMP? The Best of ONLamp.com aboutSQL Big Scary Daemons FreeBSD Basics HTTP Wrangler Linux in the Enterprise Linux Network Administration The Linux Professional Perl P5P Digest Archive PHP Admin Basics PHP Phanatics Python_News Security Alerts Alphabetical Directory of Linux Commands This directory of Linux commands is from Linux in a Nutshell, 3rd Edition. Click on any of the 379 commands below to get a description and list of available options. All links in the command summaries point to the online version of the book on Safari Tech Books Online. Buy it now Read it online expr arg1 operator arg2 [ operator arg3 … ] Evaluate arguments as expressions and print the result. Arguments and operators must be separated by spaces. In most cases, an argument is an integer, typed literally or represented by a shell variable. There are three types of operators: arithmetic, relational, and logical, as well as keyword expressions. Exit status for expr is 0 (expression is nonzero and nonnull), 1 (expression is 0 or null), or 2 (expression is invalid). Arithmetic operators Use these to produce mathematical expressions whose results are printed: + Add arg2 to arg1. - Subtract arg2 from arg1. * Multiply the arguments. / Divide arg1 by arg2. % Take the remainder when arg1 is divided by arg2. Addition and subtraction are evaluated last, unless they are grouped inside parentheses. The symbols *, (, and ) have meaning to the shell, so they must be escaped (preceded by a backslash or enclosed in single quotes). Relational operators Sponsored by:
XML Copyright 2000-2002 O’Reilly & Associates, Inc. All Rights Reserved. All trademarks and registered trademarks appearing on the O’Reilly Network are the property of their respective owners. For problems or assistance with this site, email help@oreillynet.com
O’Reilly Books Latest LAMP Titles: mod_perl Pocket Reference SQL in a Nutshell Network Printing Books by topic: Linux Open Source Security System and Network Administration Unix Web and Internet O’Reilly Network Technologies: ONJava.com ONLamp.com openp2p.com Perl.com XML.com Apache BSD Java Javascript and CSS Linux Mac Mozilla .NET P2P Perl Policy PHP Python Web Services Wireless
Sponsored by: Search | Newsletter | Conference | Tech Jobs O’Reilly’s Emerging Technology Conference: May 13-16, 2002 Articles Linux Apache MySQL Perl PHP Python BSD Essentials What is LAMP? The Best of ONLamp.com aboutSQL Big Scary Daemons FreeBSD Basics HTTP Wrangler Linux in the Enterprise Linux Network Administration The Linux Professional Perl P5P Digest Archive PHP Admin Basics PHP Phanatics Python_News Security Alerts Alphabetical Directory of Linux Commands This directory of Linux commands is from Linux in a Nutshell, 3rd Edition. Click on any of the 379 commands below to get a description and list of available options. All links in the command summaries point to the online version of the book on Safari Tech Books Online. Buy it now Read it online expand [options] files Convert tabs in given files (or standard input, if the file is named -) to appropriate number of spaces; write results to standard output. Options -tabs, -t, –tabs tabs tabs is a comma-separated list of integers that specify the placement of tab stops. If exactly one integer is provided, the tab stops are set to every integer spaces. By default, tab stops are 8 spaces apart. With -t and — tabs, the list may be separated by whitespace instead of commas. -i, –initial Convert tabs only at the beginning of lines. –help Print help message and then exit. –version Print version information and then exit. Return to: Alphabetical Directory of Linux Commands Sponsored by:
XML Copyright 2000-2002 O’Reilly & Associates, Inc. All Rights Reserved. All trademarks and registered trademarks appearing on the O’Reilly Network are the property of their respective owners. For problems or assistance with this site, email help@oreillynet.com