The dirs command output isn't that readable with many long pathnames. To make it more readable,
you could just use the -p option on dirs:
alias dirs="dirs -p"
|
Softpanorama |
May the source be with you, but remember the KISS principle ;-)
|
Nobody really knows what the Bourne shell's grammar is. Even examination of the source code is little help. |
| Tom Duff |
Bash is not particularly efficient at handling files, so consider using more appropriate tools for this within the script, such as awk or Perl.
Try to write your scripts in a structured, coherent form, so they can be reorganized and tightened up as necessary. Some of the optimization techniques applicable to high-level languages may work for scripts, but others, such as loop unrolling, are mostly irrelevant. Above all, use common sense.
The problem with bash is that it pretty baroque and there are just too many features that you need to remember. this command, that command and so on till infinity. As it is difficult to remember details of each bash has an on-line help feature that provides basic information about most of its built-in commands. To see the help description for a particular command, enter
help command
(for example, help alias) at the bash UNIX prompt. To see a list of bash commands for which help is available, type help at the bash UNIX prompt. You may access the manual page for bash by entering man bash at a UNIX prompt, but beware, it is 60 pages long and not very readable.
|
Please visit Heiner Steven SHELLdorado the best shell scripting site on the Internet |
With bash 3.x, you can reissue commands like in C-shell using arrow keys.
If you set emacs mode you can also use CTRL-p and CTRL-n to scroll through commands in your command history and use regular emacs commands to search for strings and edit a command line. For example, CTRL-d deletes a character and CTRL-k erases from the cursor to the end of the line.
Bash also supports "file name completion" which is pretty neat feature that can save some typing.
Like any decent shell Bash also allows you to define aliases and you should avoid retying the same command twice not only by browsing the history but defining aliases from history. You can define functions that are more powerful tool the aliases and can simplify repetitive jobs. You can have separate dot files with functions and aliases for example an .aliases file, and .bashrc
The dirs command output isn't that readable with many long pathnames. To make it more readable,
you could just use the -p option on dirs:
alias dirs="dirs -p"
the last argument
The arguments to a script (or function) are$1, $2, ...and can be referred to as a group by$*(or$@). But is there an easy way to refer to the last argument in list ? Try${!#}as in:echo ${!#} LAST=${!#}
a=1 echo $a # 1 a+=5 # Won't work under versions of Bash earlier than 3.1. echo $a # 15 a+=Hello echo $a # 15Hello |
Here, += functions as a string concatenation operator. Note that its behavior in this particular context is different than within a let construct.
#!/bin/bash
variable="This is a fine mess."
echo "$variable"
if [[ "$variable" =~ "T*fin*es*" ]]
# Regex matching with =~ operator within [[ double brackets ]].
then
echo "match found"
# match found
fi
|
Alternatively, the script can test for the presence of i in the $- flag.
Scripts may be forced to run in interactive mode with the i option or with a #!/bin/bash -i header. Be aware that this may cause erratic script behavior or show error messages where no error is present.
1 # Append (>>) following to end of save file. 2 date>> $SAVE_FILE #Date and time. 3 echo $0>> $SAVE_FILE #Script name. 4 echo>> $SAVE_FILE #Blank line as separator. 5 # Of course, SAVE_FILE defined and exported as environmental variable in ~/.bashrc 6 # (something like ~/.scripts-run) |
IFS Specifies internal field separators (normally space, tab, and new line) used to separate command words that result from command or parameter substitution and for separating words with the regular built-in command read. The first character of the IFS parameter is used to separate arguments for the $* substitution.
... ... ...
basename strips off the path leaving only the final component of the name, which is assumed to be the file name. If you specify suffix and the remaining portion of name contains a suffix which matches suffix, basename removes that suffix. For example
basename src/dos/printf.c .cproduces
printfdirnamereturns the directory part of the full path+name combination.Also can be done directly in bash
basename=${file##*/}
dirname=${file%/*}
Date: Tue, 12 Jan 1999 19:18:15 +0200
From: Reuben Sumner, rasumner@iname.comHere is a two cent tip that I have been meaning to submit for a long long time now.
If you have a large stack of CD-ROMS, finding where a particular file lies can be a time consuming task. My solution uses the locate program and associated utilities to build up a database of the CDs' contents that allows for rapid searching.
First we need to create the database, the following script does the trick nicely.
#!/bin/bash onedisk() { mount /mnt/cdrom find /mnt/cdrom -maxdepth 7 -print | sed "s;^/mnt/cdrom;$1;" > $1.find eject -u cdrom } echo Enter name of disk in device: read diskname while [ -n "$diskname" ]; do onedisk $diskname echo Enter name of next disk or Enter if done: read diskname done echo OK, preparing cds.db cat *.find | sort -f | /usr/lib/findutils/frcode > cds.db echo Done...Start with no CD mounted. Run the script. It will ask for a label for the CD, a short name like "sunsite1" is best. It will then quickly scan the CD, eject it and prompt for another. When you have exhausted your collection just hit enter at the prompt. A file called cds.db will be done. To make it simple to use copy cds.db to /var/lib (or anywhere else, that is where locatedb is on my system). Now create an alias likealias cdlocate="locate -d /var/lib/cds.db"Now if I type "cdlocate lyx" I getdebian20_contrib/debian/hamm/contrib/binary-i386/text/lyx_0.12.0.final-0.1.deb debian20_contrib/debian/hamm/contrib/binary-m68k/text/lyx_0.12.0.final-0.1.deb debian20_contrib/debian/hamm/contrib/source/text/lyx_0.12.0.final-0.1.diff.gz debian20_contrib/debian/hamm/contrib/source/text/lyx_0.12.0.final-0.1.dsc debian20_contrib/debian/hamm/contrib/source/text/lyx_0.12.0.final.orig.tar.gz lsa3/apps/wp/lyx-0.12.0-linux-elf-x86-libc5-bin.tar.gz lsa3/apps/wp/lyx-0.12.0.lsm lsa3/apps/wp/lyx-0.12.0.tar.gz lsa4/docs/french/www.linux-france.com/lgazette/issue-28/gx/lyx lsa4/powertools/i386/lyx-0.12.0-1.i386.rpm lsa4/powertools/SRPMS/lyx-0.12.0-1.src.rpm openlinux12/col/install/RPMS/lyx-0.11.32-1.i386.rpm openlinux12/col/sources/SRPMS/lyx-0.11.32-1.src.rpm suse53/suse/contents/lyxIn order to prevent locate from warning you that the database is old try touch -t 010100002020 /var/lib/cds.db to set the modification date to January 1 2020.--
Reuben
Ever wondered what's inside some of those binary files on your system (binary executables or binary data)? Several times I've gotten error messages from some command in the Solaris system, but I couldn't tell where the error was coming from because it was buried in some binary executable file.
The Solaris "strings" command lets you look at the ASCII text buried inside of executable files, and can often help you troubleshoot problems. For instance, one time I was seeing error messages like this when a user was trying to log in:
Could not set ULIMIT
I finally traced the problem down to the /bin/login command by running the "strings" command like this:
root> strings /bin/login | more
The strings command lists ASCII character sequences in binary files, and help me determine that the "Could not set ULIMIT" error was coming from this file. Once I determined that the error message I was seeing was coming from this file, solving the problem became a simple matter.
If you're like many Solaris users and administrators, you spend a lot of time moving back and forth between directories in similar locations. For instance, you might often work in your home directory (such as "/home/al"), the /usr/local directories, web page directories, or other user's home directories in /home.
If you're often moving back-and-forth between the same directories, and you use the Bourne shell (sh) or Korn shell (ksh) as your login shell, you can use the CDPATH shell variable to save yourself a lot of typing, and quickly move between directories.
Here's a quick demo. First move to the root directory:
cd /
Next, if it's not set already, set your CDPATH shell variable as follows:
CDPATH=/usr/spool
Then, type this cd command:
cd cron
What happens? Type this and see what happened:
pwd
The result should be "/usr/spool/cron".
When you typed "cd cron", the shell looked in your local directory for a sub-directory named "cron". When it didn't find one, it searched the CDPATH variable, and looked for a "cron" sub-directory. When it found a sub-directory named cron in the /usr/spool directory, it moved you there.
You can set your CDPATH variable just like your normal PATH variable:
CDPATH=/home/al:/usr/local:/usr/spool:/home
Have you ever needed to run a series of commands, and pipe the output of all of those commands into yet another command?
For instance, what if you wanted to run the "sar", "date", "who", and "ps -ef" commands, and wanted to pipe the output of all three of those commands into the "more" command? If you tried this:
sar -u 1 5; date; who; ps -ef | more
you'll quickly find that it won't work. Only the output of the "ps -ef" command gets piped through the "more" command, and the rest of the output scrolls off the screen.
Instead, group the commands together with a pair of parentheses (and throw in a few echo statements for readability) to get the output of all these commands to pipe into the more command:
(sar -u 1 5; echo; who; echo; ps -ef; echo; date; echo) | more
Many times it's necessary to schedule programs to run at a later time. For instance, if your computer system is very busy during the day, you may need
to run jobs late at night when nobody is logged on the system.
Solaris makes this very easy with the "at" command. You can use the "at" command to run a job at almost any time--later today, early tomorrow...whenever.
Suppose you want to run the program "my_2_hour_program" at ten o'clock tonight. Simply tell the at command to run the job at 10 p.m. (2200):
/home/al> at 2200
at> my_2_hour_program > /tmp/2hour.out
at> <CTRL><D>
warning: commands will be executed using /bin/ksh
job 890193600.a at Tue Mar 17 22:00:00 1998
Or suppose you'd like to run a find command at five o'clock tomorrow morning:
/home/al> at 0500 tomorrow
at> find /home > /tmp/find.out
at> <CTRL><D>
warning: commands will be executed using /bin/ksh
job 890215200.a at Wed Mar 18 05:00:00 1998
When you're at the "at" prompt, just type the command you want to run. Try a few tests with the at command until you become comfortable with the way
it works.
Question: How often do you create a new directory and then move into that directory in your next command? Answer: Almost always.
I realized this trend in my own work habits, so I created a simple shell function to do the hard work for me.
md () {
mkdir -p $1 && cd $1
}
This is a Bourne shell function named "md" that works for Bourne and Korn shell users. It can be easily adapted for C shell users.
Taking advantage of the -p option of the mkdir command, the function easily creates multi-level subdirectories, and moves you into the lowest level of the directory structure. You can use the command to create one subdirectory like this:
/home/al> md docs
/home/al/docs> _
or you can create an entire directory tree and move right into the new directory like this:
/home/al> md docs/memos/internal/solaris8
/home/al/docs/memos/internal/solaris8>
Date: Fri, 15 Jan 1999 19:55:51 +0100 (CET)
From: JL Hopital, cdti94@magic.frMy English is terrible,so feel free to correct if you decide to publish...
Hello,i am a French linuxer and here is my two cent tips. If you have many CD-ROMs and want to retrieve this_file_I'm_sure_i_have_but_can't_remember_where, it can helps.
It consist of 2 small scripts using gnu utilities: updatedb and locate. Normally 'updatedb' run every night, creating a database for all the mounted file systems and 'locate' is used to query this system-wide database.But you can tell them where are the files to index and where to put the database.That's what my scripts does:
The first script (addcd.sh) create a database for the cd actually mounted.You must run it once for every cdrom.
The second ( cdlocate.sh ) search in the databases created by addcd.sh and display the cdname and full path of the files matching the pattern you give in parameter. So you can search for unmounted files !
To use:
Beware that locate's regular expressions have some peculiarities, 'man locate' will explain.
- create a directory and copy in it the 2 scripts
mkdir /home/cdroms cp addcd.sh cdlocate.sh /home/cdroms- mount the first cdrom you want to index
mount /mnt/cdrom( if your mount point is different , you must adapt the script )- run addcd.sh with a fully descriptive name for this cdrom as parameter (this description will be used as part of the database name ,don't use space):
./addcd.sh Linux.Toolkit.Disk1.Oct.1996It will take some time to updatedb to create the databases specially if the cdrom contain many files.- umount the cdrom and go to step 2 for all the cdroms you want or every time you've got a new one(I have more than 70 databases created this way).
- you can now use cdlocate.sh,to retrieve files
./cdlocate.sh '*gimp*rpm'Hope this help and happy linuxing !
---Cut here------------------------------ # addcd.sh # Author: Jose-Luc.Hopital@ac-creteil.fr # Create a filename's database in $DATABASEHOME for the cd mounted # at $MOUNTPOINT # Example usage: addcd.sh Linux.Toolkit.Disk3.Oct.1996 # to search the databases use cdlocate.sh CDNAME=$1 test "$CDNAME" = "" && { echo Usage:$0 name_of_cdrom ; exit 1 ; } # the mount point for the cd-ROM MOUNTPOINT=/mnt/cdrom # where to put the database DATABASEHOME=/home/cdroms updatedb --localpaths=$MOUNTPOINT --output=$DATABASEHOME/$CDNAME.updatedb && \ echo Database added for $CDNAME ---Cut here-------------------------------- # cdlocate.sh # Author : Jose-Luc.Hopital@ac-creteil.fr # Usage $0 pattern # search regular expression in $1 in the database's found in $DATABASEHOME # to add a database for a new cd-rom , use addcd.sh test "$*" = "" && { echo Usage:$0 pattern ; exit 1 ; } DATABASEHOME=/home/cdroms cd $DATABASEHOME # get ride of locate warning:more than 8 days old touch *.updatedb CDROMLIST=`ls *.updatedb` for CDROM in $CDROMLIST do CDROMNAME=`basename $CDROM .updatedb` locate --database=$DATABASEHOME/$CDROM $@ |sed 's/^/'$CDROMNAME:'/' done
bash Cookbook Reader - Contributions browse
String expansion
Indirect variable references - the new way
1 #!/bin/bash 2 3 # Indirect variable referencing. 4 # This has a few of the attributes of references in C++. 5 6 7 a=letter_of_alphabet 8 letter_of_alphabet=z 9 10 # Direct reference. 11 echo "a = $a" 12 13 # Indirect reference. 14 echo "Now a = ${!a}" 15 # The ${!variable} notation is greatly superior to the old "eval var1=\$$var2" 16 17 echo 18 19 t=table_cell_3 20 table_cell_3=24 21 echo "t = ${!t}" 22 table_cell_3=387 23 echo "Value of t changed to ${!t}" 24 # Useful for referencing members 25 # of an array or table, 26 # or for simulating a multi-dimensional array. 27 # An indexing option would have been nice (sigh). 28 29 30 exit 0
Using arrays and other miscellaneous trickery to deal four random hands from a deck of cards
1 #!/bin/bash2 2 # Must specify version 2 of bash, else might not work. 3 4 # Cards: 5 # deals four random hands from a deck of cards. 6 7 UNPICKED=0 8 PICKED=1 9 10 DUPE_CARD=99 11 12 LOWER_LIMIT=0 13 UPPER_LIMIT=51 14 CARDS_IN_SUITE=13 15 CARDS=52 16 17 declare -a Deck 18 declare -a Suites 19 declare -a Cards 20 # It would have been easier and more intuitive 21 # with a single, 3-dimensional array. Maybe 22 # a future version of bash will support 23 # multidimensional arrays. 24 25 26 initialize_Deck () 27 { 28 i=$LOWER_LIMIT 29 until [ $i -gt $UPPER_LIMIT ] 30 do 31 Deck[i]=$UNPICKED 32 let "i += 1" 33 done 34 # Set each card of "Deck" as unpicked. 35 echo 36 } 37 38 initialize_Suites () 39 { 40 Suites[0]=C #Clubs 41 Suites[1]=D #Diamonds 42 Suites[2]=H #Hearts 43 Suites[3]=S #Spades 44 } 45 46 initialize_Cards () 47 { 48 Cards=(2 3 4 5 6 7 8 9 10 J Q K A) 49 # Alternate method of initializing array. 50 } 51 52 pick_a_card () 53 { 54 card_number=$RANDOM 55 let "card_number %= $CARDS" 56 if [ ${Deck[card_number]} -eq $UNPICKED ] 57 then 58 Deck[card_number]=$PICKED 59 return $card_number 60 else 61 return $DUPE_CARD 62 fi 63 } 64 65 parse_card () 66 { 67 number=$1 68 let "suite_number = number / CARDS_IN_SUITE" 69 suite=${Suites[suite_number]} 70 echo -n "$suite-" 71 let "card_no = number % CARDS_IN_SUITE" 72 Card=${Cards[card_no]} 73 printf %-4s $Card 74 # Print cards in neat columns. 75 } 76 77 seed_random () 78 { 79 # Seed random number generator. 80 seed=`eval date +%s` 81 let "seed %= 32766" 82 RANDOM=$seed 83 } 84 85 deal_cards () 86 { 87 echo 88 89 cards_picked=0 90 while [ $cards_picked -le $UPPER_LIMIT ] 91 do 92 pick_a_card 93 t=$? 94 95 if [ $t -ne $DUPE_CARD ] 96 then 97 parse_card $t 98 99 u=$cards_picked+1 100 # Change back to 1-based indexing (temporarily). 101 let "u %= $CARDS_IN_SUITE" 102 if [ $u -eq 0 ] 103 then 104 echo 105 echo 106 fi 107 # Separate hands. 108 109 let "cards_picked += 1" 110 fi 111 done 112 113 echo 114 115 return 0 116 } 117 118 119 # Structured programming: 120 # entire program logic modularized in functions. 121 122 #================ 123 seed_random 124 initialize_Deck 125 initialize_Suites 126 initialize_Cards 127 deal_cards 128 129 exit 0 130 #================ 131 132 133 134 # Exercise 1: 135 # Add comments to thoroughly document this script. 136 137 # Exercise 2: 138 # Revise the script to print out each hand sorted in suites. 139 # You may add other bells and whistles if you like. 140 141 # Exercise 3: 142 # Simplify
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Last modified: April 04, 2008