- Copyright
- PREFACE
- Acknowldgements
- About the Author
- Introduction to Linux Shells
- The Linux Tool Box
- The Grep Family (Gnu & Sons)
- The Streamlined Editor
- Gawk Utility: Gawk as a Linux Tool
- The Gawk Utility: Evaluating Expressions
- The Gawk Utility: Gawk Programming
- The Interactive Bash Shell
- Programming with the Bash Shell
- Introduction
- Reading User Input
- Arithmetic
- Positional Parameters and Command Line Arguments
- Conditional Constructs and Flow Control
- Looping Commands
- Functions
- Trapping Signals
- Debugging
- Processing Command Line Options with getopts
- The eval Command and Parsing the Command Line
- Bash Options
- Shell Built-In Commands
- The Bash Shell Lab Exercises
- The Interactive TC Shell
- Programming with the TC Shell
- Useful Linux/UNIX Utilities for Shell Programmers
- apropos—searches the what is database for strings
- arch—prints the machine architecture (see uname -m)
- at—at, atq, atrmbatch—execute commands at a later time
- awk (gawk)—pattern scanning and processing language
- banner—make posters
- basename—with a directory name delivers portions of the pathname
- bash—Gnu Bourne Again Shell
- bc—processes precision arithmetic
- biff [ny]—be notified if mail arrives and who it is from
- cal—displays a calendar
- cat—concatenates and displays files
- chfn—change the finger information
- chmod—change the permissions mode of a file
- chown—change the user and group ownership of files
- chsh—change your login shell
- clear—clears the terminal screen
- cmp—compares two files
- compress—compress, uncompress, zcat compress, uncompress files, or display expanded files
- cp—copies files
- cpio—copy file archives in and out
- cron—the clock daemon
- crypt—encodes or decodes a file
- cut—removes selected fields or characters from each line of a file
- date—displays the date and time or sets the date
- dd—converts a file while copying it
- diff—compares two files for differences
- dos, xdos, dosexec, dosdebug—a Linux dos emulator that runs MS-DOS and MS-DOS programs under Linux
- df—summarizes free disk space
- du-summarizes disk usage
- echo—echoes arguments
- egrep—searches a file for a pattern using full regular expressions
- expr—evaluates arguments as an expression.
- fgrep—search a file for a character string
- file—determines the type of a file by looking at its contents
- find—finds files
- finger—displays information about local and remote users
- fmt—simple text formatters
- fold—folds long lines
- ftp—file transfer program
- free—displays amount of free and used memory in the system
- fuser—identifies processes using files or sockets
- gawk—pattern scanning and processing language
- gcc, g++—Gnu project C and C++ Compiler (v2.7)
- getopt(s)—parses command line options
- grep—searches a file for a pattern (See Chapter 3)
- groups—prints group membership of user
- gzip, gunzip, zcat—compresses or expands files
- head—outputs the first ten lines of a file(s)
- host—prints information about specified hosts or zones in DNS
- id—prints the username, user ID, group name, and group ID
- jsh—the standard, job control shell
- kill—sends a signal to terminate one or more processes
- killall—kills processes by name
- less—opposite of more
- line—reads one line
- ln—creates hard links to files
- logname—gets the name of the user running the process
- look—displays lines beginning with a given string
- lp (ATT, Linux)—sends output to a printer
- lpr (UCB, Linux)—sends output to a printer
- lpstat (ATT)—prints information about the status of the LP print service
- lpq (UCB, Linux)—prints information about the status of the printer
- ls, dir, vdir—lists contents of directory
- mail—mail, rmail—reads mail or send mail to users
- mailx—interactive message processing system
- make—maintains, updates, and regenerates groups of related programs and files
- man—formats and displays the online manual pages
- manpath—determines user's search path for man pages
- mesg—permits or denies messages resulting from the write command
- mkdir—creates a directory
- more—browses or pages through a text file
- mtools—utilities to access DOS disks in UNIX
- mv—moves or renames files
- nawk—pattern scanning and processing language
- newgrp—logs in to a new group
- news—prints news items
- nice—runs a command at low priority
- nohup—makes commands immune to hangups and quits
- od—dumps files in octal and other formats
- pack—pack, pcat, unpack—compresses and expands files
- passwd—changes the login password and password attributes
- paste—merges same lines of several files or subsequent lines of one file
- pcat—(see "pack" on page706)
- pine—a Program for Internet News and E-mail
- pg—displays files a page at a time
- pr—prints files
- ping—reports if a remote system is reachable and alive
- ps—reports process status
- pstree—displays a tree of processes
- pwd—displays the present working directory name
- quota—displays users' disk usage and limits
- rcp—remote file copy
- rdate—get the date and time via the network
- rgrep—a recursive, highlighting grep program
- rlogin—remote login
- rm—removes files from directories
- rmdir—removes a directory
- rsh—starts a remote shell
- ruptime—shows the host status of local machines
- rwho—who is logged in on local machines
- script—creates a typescript of a terminal session
- sed—stream editor (seeChapter 4)
- size—prints section sizes in bytes of object files
- sleep—suspends execution for some number of seconds
- sort—sort and/or merge files
- spell—finds spelling errors
- split—splits a file into pieces
- strings—finds any printable strings in an object or binary file
- stty—sets the options for a terminal
- su—become superuser or another user
- sum—calculates a checksum for a file
- sync—updates the superblock and sends changed blocks to disk
- tabs—sets tab stops on a terminal
- tail—displays the tail end of a file
- talk—allows you to talk to another user
- tar—stores and retrieves files from an archive file, normally a tape device
- tee—replicates the standard output
- telnet—communicates with a remote host
- test—evaluates an expression and check file types
- time—displays a summary of time used by this shell and its children
- timex—times a command; reports process data and system activity
- top—displays top CPU processes
- touch—updates access time and/or modification time of a file
- tput—initializes a terminal or queries the terminfo database
- tr—translates characters
- true—provides successful exit status
- tsort—topological sort
- tty—gets the name of the terminal
- umask—sets file-creation mode mask for permissions
- uname—prints name of current machine
- uncompress—restores files to their original state after they have been compressed using the compress command
- uniq—reports on duplicate lines in a file
- units—converts quantities expressed in standard scales to other scales
- unpack—expands files created by pack
- uucp—copies files to another system, UNIX-to-UNIX system copy
- uuencode—uuencode, uudecode—encodes a binary file into ASCII text in order to send it through e-mail, or convert it back into its original form
- wc—counts lines, words, and characters
- what—extracts SCCS version information from a file by printing information found after the @(#) pattern
- which (UCB)—locates a command and displays its pathname or alias
- whereis (UCB)—locates the binary, source, and manual page files for a command
- who—displays who is logged on the system
- write—writes a message to another user
- xargs—constructs an argument list(s) and executes a command
- zcat—uncompresses a compressed file to standard output. Same as uncompress –c
- zipinfo—lists detailed information about a ZIP archive
- zmore—file perusal filter for crt viewing of compressed text
- Comparison of the Shells
- Steps for Using Quoting Correctly
- Index
expr—evaluates arguments as an expression.
expr expression…
expr {--help,--version}
The arguments are taken as an expression. After evaluation, the result is written on the standard output. The terms of the expression must be separated by blanks. Characters special to the shell must be escaped. Used in Bourne shell scripts for performing simple arithmetic operations.
Example A.24.
1 expr 5 + 4 2 expr 5 * 3 3 num=0 num=`expr $num + 1` |
Explanation
Prints the sum of 5 + 4.
Prints of result of 5 * 3. The asterisk is protected from shell expansion.
After assigning 0 to variable num, the expr command adds 1 to num and the result is assigned to num.
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