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Posts Tagged ‘bash’

bash has a great feature called dynamic-complete-history that will allow you to complete text at point with contents from your bash history list.

examine the following workflow :

$ touch file1.txt file-with-a-long-name.txt file3.txt
$ some commands
$ some more commands
$ change directory
$ touch file…

at this point you want to type touch file-with-a-long-name.txt to create another file with the same name in the new directory. would it not be great if i could hit a few characters and then magically complete the name just like hitting TAB in bash completes filenames. yes you can using the bash feature dynamic-complete-history.

just write

$ touch file

and then hit C-M-i (Ctrl+Alt+i) and bash will try to complete the the file name by scanning through the history list. if there are multiple matches then it will display all matching items. enter some more characters until u get a unique match and then hit C-M-i.

the gist of the matter is that if you have already typed some thing and it is in the history list then you can insert it at point with ease. this saves typing which is a good thing.

at first i wrongly assumed that this feature was provided by the gnu readline library but on examining the man page of readline i could not find the corresponding documentation. it turns out that this is a feature provided by bash. on reading the man page of bash i found that it is bound to the key M-TAB but on gnome3 M-TAB is the task switcher i.e. it cycles between open applications. fortunately the magic key chord “\M-\C-i” (Alt+Ctrl+i) is also bound to dynamic-complete-history. this i found out by examining the output of bind -p. i have no idea where this binding is defined

to learn more about bind try

$ help bind

yes that is a help not man

bash version i tested this on is GNU bash, version 4.2.24(2)-release (i686-pc-linux-gnu)

the M in the key chord is the Meta key which is the Alt key on my keyboard.

point basically means where your cursor is at.

bash history list is not the same as ~/.bash_history

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there have been some situations where i needed a custom grid on a 2-dimensional plot in gnuplot instead of a regularly placed grid. in order for me to set up a customized grid i have to first set up a customised xtics and/or ytics. gnuplot does provide a way of providing user preferred tics by manually typing them in at the gnuplot command prompt:

gnuplot> set xtics (1,2,3,4)

however that might get too tiresome for your digits. naturally one would want to employ the powerful text processors and stream editors that GNU/Linux provides. this is how i went about it:

assume that the data file(data.out, say) is as follows:

# some comments and blank lines

#      #x1	#x2 	  #x3

1      1.1	3.9	  4.5
2      2.7	6.1	  5.6
3      3.9	2.3	  3.4
       
4      3.5	4.3	  34.0
5      12.1	3.4	  15.9

i want to set the xtics to the values in column 2 and ytics to the values in column 3 say. first i conjure up the following shell script (ttf.sh, say):

#!/usr/bin/env bash

# set tic levels from file at the gnuplot prompt
# examples:
# gnuplot> `./tff.sh data.dat 1 xtics`
# gnuplot> `./tff.sh data.dat 2 ytics`

# dataFile from which tic levels will be read
dataFile=$1

# which column to use
column=$2

# xtics OR ytics 
whichTics=$3

sed -e '/^#/d' $dataFile | \
    sed -e '/^$/d' | \
    cut -f $column | \
    tr '\n' ',' | \
    sed -e "s/^/set $whichTics (/" | \
    sed -e 's/,$/)\n/'

and then in gnuplot carry out the following sequence of commands:

gnuplot> `./tff.sh data.out 2 xtics`
gnuplot> `./tff.sh data.out 3 ytics`
gnuplot> plot 'data.out' u 1:2 w p pt 13 ps 2

to produce the following plot:

it should be noted that some of the grid lines are hidden due to alignment with borders.

the shell script needs 3 inputs

  1. datafile name
  2. which column to pull from the datafile
  3. which tics to set the values to

then the whole command is sandwiched between couple of backtics which bring in the command substitution magic. one could very well do the following in bash:

$ ./tff.sh data.out 2 xtics > tmp

and then in gnuplot

gnuplot> load 'tmp'

but i prefer the backtics.

now the explanation of the wonderful sed magic. first we do a little bit of file cleaning/processing like removing comments and blank lines. these operations may not necessarily apply to your case or might need additional operations which is not that difficult a job. anyways on to the explanations now…

sed -e '/^#/d' $dataFile

simply deletes all lines starting with the # symbol. of course if the comment character is different one should change the code appropriately. ^ stands for the beginning of all lines and ^# means all lines starting with a # symbol. the `d’ command instructs sed to delete those lines. we then pipe (|) the output of this command to the next command

 
sed -e '/^$/d' 

which simply deletes all blank lines. since ^ represents the beginning of all lines and $ represents the end of all lines, ^$ then represents those lines with nothing in between ^ and $ i.e. blank lines. as always the `d’ command instructs sed to delete this line.

cut -f $column

next we cut out the required column from the datafile using the cut command. we assume here that the field separater is a TAB character. if some other field separater is being used that can be specified with the -d switch. do a `man cut` to find out more. now comes the all important part of the entire exercise, what we want is to transform the vertical stack of values:

1
2
3

to a horizontal comma separated list of values:

1,2,3,

notice the comma after 3.
we achieve this by using the tr command which we instruct to transform all the newline characters (`\n’) to the comma character (`,’). we do pick up an unwanted comma at the very end of the list which we get rid of and transformed to a right bracket ) like so:

sed -e 's/,$/)\n/'

this time we are using the subsitute command `s’ and asking sed to replace the last comma by a ). as you already know $ represents the end of the line so (,$) represents the last comma we substitute those with a right bracket ) and a newline character `\n’.
of course we had to prepend the “set xtics (” to the beginning of the list and that bit is done by the following:

sed -e "s/^/set $whichTics (/"

notice the double quotes instead of the single quotes. we use double quotes so that $whichTics is automatically expanded to the user supplied tics name.

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let me first describe the problem that way annoying me for a long long long time.

i use tmux and do my compiling and coding in one window and then many a times i need to open a new window to do some other stuff. the problem i face is that the bash commands that i write in one window are not present in the new window’s bash history.

for example note a typical annoyance

cd code/genetic/convergence/zdt1/population100/

do some work and then create a new window in tmux (C-b c) in order to do some work in the same directory.

and now most probably you will be placed in your home folder if that is where you started tmux initially.  so now in the new window i have to do this long change directory command.  the long cd command will not be written to bash history unless the shell exits.

this was a major annoyance to me for a long time. i wanted all the bash sessions to share the history concurrently.  i found a hack which lets me do what i want.

put the following in your .bashrc

export PROMPT_COMMAND="$PROMPT_COMMAND; history -a"
shopt -s histappend

If the histappend shell option is enabled the lines are appended to the history file, otherwise the history file is overwritten. to find out more about histappend just do a man bash and search for histappend.

the history command we refer to here is the bash built-in history command to know more about it do a

help history

yes that is help history **not** man history

if i have understood it correctly i guess the cleverness of the hack is in automatically doing a “history -a” after each command and what better way than to modify the PROMPT_COMMAND which defines how the prompt should be constructed each time. sweet 🙂

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emacs maximized

back when i was on ubuntu hardy heron i used the following in my .emacs to maximize the emacs window on startup

;;i tried the following with ``emacs -nw" and it does not work
 (defun toggle-fullscreen ()
   (interactive)
   (x-send-client-message nil 0 nil "_NET_WM_STATE" 32
 	    		 '(2 "_NET_WM_STATE_MAXIMIZED_VERT" 0))
   (x-send-client-message nil 0 nil "_NET_WM_STATE" 32
 			 '(2 "_NET_WM_STATE_MAXIMIZED_HORZ" 0))
   )
(toggle-fullscreen)

now that i am on archlinux with emacs 23.2.1 i follow a different strategy

i have defined the following function in my .bashrc

function e()
{
    # i was advised to not use $*
    emacs --maximized "$@" &
}

the reason i defined a function and not an alias is so that i can use the & at the end.

this works great.

i just wanted to make this post for reference as i m modifying my .emacs

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task at hand

you have two files :: file1.txt and file2.txt

you want to insert the contents of file1.txt into file2.txt starting at line number 2

contents of file1.txt before the process

because i m stupid

contents of file2.txt before the process

why do you want to do a phd ?

ok then, may god rest your spirit in peace.

contents of file2.txt after the process

why do you want to do a phd ?

because i m stupid

ok then, may god rest your spirit in peace.

this is how you do it

sed ‘2r file1.txt’ < file2.txt > tempFile.txt

mv tempFile.txt file2.txt

the r stands for the read FILENAME command and is a GNU extension i believe. so it may not be available on all platforms. to find out more try
info sed
and in particular see the section 3.6 Less Frequently-Used Commands

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