Advanced Bash−Scripting Guide

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#!/bin/bash # keypress.sh: Detect a user keypress ("hot keyboard"). echo Advanced Bash−Scripting Guide old_tty_settings=$(stty −g) stty −icanon Keypress=$(head −c1) # Save old settings. # or $(dd bs=1 count=1 2> /dev/null) # on non−GNU systems echo echo "Key pressed was \""$Keypress"\"." echo stty "$old_tty_settings" # Restore old settings. # Thanks, Stephane Chazelas. exit 0 Also see Example 9−3. terminals and modes Normally, a terminal works in the canonical mode. When a user hits a key, the resulting character does not immediately go to the program actually running in this terminal. A buffer local to the terminal stores keystrokes. When the user hits the ENTER key, this sends all the stored keystrokes to the program running. There is even a basic line editor inside the terminal. bash$ stty −a speed 9600 baud; rows 36; columns 96; line = 0; intr = ^C; quit = ^\; erase = ^H; kill = Û; eof = ^D; eol = ; eol2 = ; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; flush = Ô; ... isig icanon iexten echo echoe echok −echonl −noflsh −xcase −tostop −echoprt Using canonical mode, it is possible to redefine the special keys for the local terminal line editor. bash$ cat > filexxx whaIfoo barhello world bash$ cat filexxx hello world bash$ bash$ wc −c < file 13 The process controlling the terminal receives only 13 characters (12 alphabetic ones, plus a newline), although the user hit 26 keys. In non−canonical ("raw") mode, every key hit (including special editing keys such as ctl−H) sends a character immediately to the controlling process. Chapter 13. System and Administrative Commands 218
Advanced Bash−Scripting Guide The Bash prompt disables both icanon and echo, since it replaces the basic terminal line editor with its own more elaborate one. For example, when you hit ctl−A at the Bash prompt, there's no Â echoed by the terminal, but Bash gets a \1 character, interprets it, and moves the cursor to the begining of the line. tset Stephane Chazelas Show or initialize terminal settings. This is a less capable version of stty. bash$ tset −r Terminal type is xterm−xfree86. Kill is control−U (Û). Interrupt is control−C (^C). setserial Set or display serial port parameters. This command must be run by root user and is usually found in a system setup script. # From /etc/pcmcia/serial script: IRQ=`setserial /dev/$DEVICE | sed −e 's/.*IRQ: //'` setserial /dev/$DEVICE irq 0 ; setserial /dev/$DEVICE irq $IRQ getty, agetty The initialization process for a terminal uses getty or agetty to set it up for login by a user. These commands are not used within user shell scripts. Their scripting counterpart is stty. mesg Enables or disables write access to the current user's terminal. Disabling access would prevent another user on the network to write to the terminal. wall It can be very annoying to have a message about ordering pizza suddenly appear in the middle of the text file you are editing. On a multi−user network, you might therefore wish to disable write access to your terminal when you need to avoid interruptions. This is an acronym for "write all", i.e., sending a message to all users at every terminal logged into the network. It is primarily a system administrator's tool, useful, for example, when warning everyone that the system will shortly go down due to a problem (see Example 17−2). bash$ wall System going down for maintenance in 5 minutes! Broadcast message from bozo (pts/1) Sun Jul 8 13:53:27 2001... System going down for maintenance in 5 minutes! dmesg If write access to a particular terminal has been disabled with mesg, then wall cannot send a message to it. Lists all system bootup messages to stdout. Handy for debugging and ascertaining which device drivers were installed and which system interrupts in use. The output of dmesg may, of course, be parsed with grep, sed, or awk from within a script. bash$ dmesg | grep hda Kernel command line: ro root=/dev/hda2 hda: IBM−DLGA−23080, ATA DISK drive Chapter 13. System and Administrative Commands 219
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Chapter 1. Why Shell Programming? A
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Chapter 2. Starting Off With a Sha
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Chapter 3. Special Characters Speci
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# Sometimes, though, you get: # 11
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The "−" can be used to pipe stdou
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change the behavior of the terminal
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Chapter 4. Introduction to Variable
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The shift command reassigns the pos
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Example 5−1. Echoing Weird Variab
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(cd /source/directory && tar cf −
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true # the "true" builtin. echo "ex
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Advanced Bash−Scripting Guide if
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if [[ −e $file ]] then echo "Pass
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Advanced Bash−Scripting Guide −
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7.3. Comparison operators (binary)
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Example 7−5. arithmetic and strin
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Chapter 8. Operations and Related T
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Advanced Bash−Scripting Guide ! ^
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Part 3. Beyond the Basics Table of
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$EDITOR the default editor invoked
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Advanced Bash−Scripting Guide (Th
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Advanced Bash−Scripting Guide #!/
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Example 9−2. Timed Input Advanced
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Advanced Bash−Scripting Guide fi
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echo 'IFS=":", using "$@"' c=0 for
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Advanced Bash−Scripting Guide use
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echo '${var1#$pattern1} =' "${var1#
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t=${path_name%/*.*} # Same effect a
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Chapter 10. Loops and Branches Oper
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Advanced Bash−Scripting Guide OUT
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As is the case with for/in loops, p
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This construct tests for a conditio
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Advanced Bash−Scripting Guide ###
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# Accept upper or lowercase input.
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Advanced Bash−Scripting Guide a=`
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# May need to also press ENTER if a
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cat, tac # Burn the CDR. cdrecord
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Advanced Bash−Scripting Guide 12.
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exit $E_CHANGED_MIND ;; *) echo "De
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The multiplication operator must be
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echo Number of digits at the beginn
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Outputs very verbose timing statist
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This line occurs three times. This
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# List all the users in /etc/passwd
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Advanced Bash−Scripting Guide # r
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# Range: 0 − 200 # It's crude, bu
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Advanced Bash−Scripting Guide alt
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# grep PATTERN /etc/passwd | awk
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Advanced Bash−Scripting Guide # Y
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Chapter 25. List Constructs The "an
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# AND LIST executes on true, OR LIS
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echo ${colors[$index]} let "index =
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# Replace all matching wildcarded s
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fi let "t += $i " Primes[t]=$NON_PR
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Advanced Bash−Scripting Guide # =
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# −−−−−−−−− # 1)
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Chapter 28. /dev and /proc A Linux
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Advanced Bash−Scripting Guide # A
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Chapter 30. Debugging The Bash shel
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4. Advanced Bash−Scripting Guide
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Chapter 31. Options Options are set
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Chapter 32. Gotchas Turandot: Gli e
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command1 2> − | command2 # Trying
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echo "one two three" | read a b c #
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Chapter 33. Scripting With Style Ge
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#!/bin/bash # color−echo.sh: Echo
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34.7. Assorted Tips Advanced Bash
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Advanced Bash−Scripting Guide the
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Advanced Bash−Scripting Guide •
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# agram.sh: Playing games with anag
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Chapter 35. Bash, version 2 The cur
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Advanced Bash−Scripting Guide # R
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1−56592−580−7). This is the s
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Bibliography Edited by Peter Dennin
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Advanced Bash−Scripting Guide * A
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Mark Komarinski's Printing−Usage
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let "row = $r" # Count center row o
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next_gen "$Cur" let "generation +=
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[−c localdirectory] [−m filepat
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Advanced Bash−Scripting Guide #:d
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# ListDirectory "FileGlob" "Field
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Advanced Bash−Scripting Guide # I
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The md5sum program is documented as
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Note: 'mount −l' does return the
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Advanced Bash−Scripting Guide dec
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Appendix B. A Sed and Awk Micro−P
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Advanced Bash−Scripting Guide Tha
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Appendix D. A Detailed Introduction
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Appendix E. Localization Localizati
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Appendix F. History Commands The Ba
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Advanced Bash−Scripting Guide } X
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Appendix H. Converting DOS Batch Fi
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Appendix I. Exercises I.1. Analyzin
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Lottery Numbers One type of lottery
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Advanced Bash−Scripting Guide Usi
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Advanced Bash−Scripting Guide and
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[33] This is actually a script adap
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# Thanks to Stephane Chazelas for p
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