- 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
awk (gawk)—pattern scanning and processing language
gawk [ POSIX or Gnu style options ] –f program–file [ - ] file…
awk scans each input filename for lines that match any of a set of patterns specified in prog. (See Chapter 5, "The gawk Utility: gawk as a Linux Tool." ) In the following example, use awk, nawk, or gawk, depending on your version of awk.
Example A.4.
1 awk '{print $1, $2}' file
2 awk '/John/{print $3, $4}' file
3 awk -F: '{print $3}' /etc/passwd
4 date | awk '{print $6}'
|
Explanation
Prints the first two fields of file where fields are separated by white space.
Prints fields 3 and 4 if the pattern John is found.
Using a colon as the field separator, prints the third field of the /etc/passwd file.
Sends the output of the date command to awk and prints the sixth field.
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