Commands tagged variable (19)

  • Run the alias command, then issue ps aux | head and resize your terminal window (putty/console/hyperterm/xterm/etc) then issue the same command and you'll understand. ${LINES:-`tput lines 2>/dev/null||echo -n 12`} Insructs the shell that if LINES is not set or null to use the output from `tput lines` ( ncurses based terminal access ) to get the number of lines in your terminal. But furthermore, in case that doesn't work either, it will default to using the deafault of 12 (-2 = 10). The default for HEAD is to output the first 10 lines, this alias changes the default to output the first x lines instead, where x is the number of lines currently displayed on your terminal - 2. The -2 is there so that the top line displayed is the command you ran that used HEAD, ie the prompt. Depending on whether your PS1 and/or PROMPT_COMMAND output more than 1 line (mine is 3) you will want to increase from -2. So with my prompt being the following, I need -7, or - 5 if I only want to display the commandline at the top. ( http://www.askapache.com/linux-unix/bash-power-prompt.html ) 275MB/748MB [7995:7993 - 0:186] 06:26:49 Thu Apr 08 [askapache@n1-backbone5:/dev/pts/0 +1] ~ In most shells the LINES variable is created automatically at login and updated when the terminal is resized (28 linux, 23/20 others for SIGWINCH) to contain the number of vertical lines that can fit in your terminal window. Because the alias doesn't hard-code the current LINES but relys on the $LINES variable, this is a dynamic alias that will always work on a tty device. Show Sample Output


    26
    alias head='head -n $((${LINES:-`tput lines 2>/dev/null||echo -n 12`} - 2))'
    AskApache · 2010-04-08 22:37:06 7
  • substrings a variable starting at position. If no offset given prints rest of the line Show Sample Output


    12
    var='123456789'; echo ${var:<start_pos>:<offset>}
    totti · 2011-09-14 20:05:17 2
  • Use `sysctl -p` without argument will only load /etc/sysctl.conf, but user configs always put in /etc/sysctl.d/*.conf, `sysctl --system` will load all the config files


    7
    sysctl --system
    tankywoo · 2015-01-29 07:56:36 1
  • Also resolves symlinks, showing the full path of the link target


    3
    BASEDIR=$(dirname $(readlink -f $0))
    mackaz · 2011-12-01 09:10:21 0
  • This uses some tricks I found while reading the bash man page to enumerate and display all the current environment variables, including those not listed by the 'env' command which according to the bash docs are more for internal use by BASH. The main trick is the way bash will list all environment variable names when performing expansion on ${!A*}. Then the eval builtin makes it work in a loop. I created a function for this and use it instead of env. (by aliasing env). This is the function that given any parameters lists the variables that start with it. So 'aae B' would list all env variables starting wit B. And 'aae {A..Z} {a..z}' would list all variables starting with any letter of the alphabet. And 'aae TERM' would list all variables starting with TERM. aae(){ local __a __i __z;for __a in "$@";do __z=\${!${__a}*};for __i in `eval echo "${__z}"`;do echo -e "$__i: ${!__i}";done;done; } And my printenv replacement is: alias env='aae {A..Z} {a..z} "_"|sort|cat -v 2>&1 | sed "s/\\^\\[/\\\\033/g"' From: http://www.askapache.com/linux-unix/bash_profile-functions-advanced-shell.html Show Sample Output


    2
    for _a in {A..Z} {a..z};do _z=\${!${_a}*};for _i in `eval echo "${_z}"`;do echo -e "$_i: ${!_i}";done;done|cat -Tsv
    AskApache · 2010-10-27 07:16:54 0
  • Will use variable value (for variable $my_dir, in this case), an assign a default value if there is none. Show Sample Output


    2
    ls ${my_dir:=/home}
    robinsonaarond · 2011-11-30 15:06:51 0
  • Run the alias command, then issue ps aux | tail and resize your terminal window (putty/console/hyperterm/xterm/etc) then issue the same command and you'll understand. ${LINES:-`tput lines 2>/dev/null||echo -n 12`} Insructs the shell that if LINES is not set or null to use the output from `tput lines` ( ncurses based terminal access ) to get the number of lines in your terminal. But furthermore, in case that doesn't work either, it will default to using the default of 80. The default for TAIL is to output the last 10 lines, this alias changes the default to output the last x lines instead, where x is the number of lines currently displayed on your terminal - 7. The -7 is there so that the top line displayed is the command you ran that used TAIL, ie the prompt. Depending on whether your PS1 and/or PROMPT_COMMAND output more than 1 line (mine is 3) you will want to increase from -2. So with my prompt being the following, I need -7, or - 5 if I only want to display the commandline at the top. ( http://www.askapache.com/linux/bash-power-prompt.html ) 275MB/748MB [7995:7993 - 0:186] 06:26:49 Thu Apr 08 [askapache@n1-backbone5:/dev/pts/0 +1] ~ In most shells the LINES variable is created automatically at login and updated when the terminal is resized (28 linux, 23/20 others for SIGWINCH) to contain the number of vertical lines that can fit in your terminal window. Because the alias doesn't hard-code the current LINES but relys on the $LINES variable, this is a dynamic alias that will always work on a tty device. Show Sample Output


    2
    alias tail='tail -n $((${LINES:-`tput lines 2>/dev/null||echo -n 80`} - 7))'
    AskApache · 2012-03-22 02:44:11 2
  • Reload all defined kernel variables from /etc/sysctl.conf(if no parameter after -p is given) without the old myth "Ah, you'll need to reboot to apply those variables"... Show Sample Output


    1
    /sbin/sysctl -p
    Risthel · 2013-02-14 12:48:26 0
  • See "Parameter Expansion" in the bash manpage. They refer to this as "Use Alternate Value", but we're including the var in the at alternative. Show Sample Output


    1
    command ${MYVAR:+--someoption=$MYVAR}
    pdxdoughnut · 2015-11-04 19:47:24 0
  • You define your variable MYVAR with the desired search pattern: MYVAR= ...which can then be searched with the find command. This is useful if you in a script, where you want the arguments to be fed into the find command. The provided search is case insensitive (-iname) and will find all files and directories with the pattern MYVAR (not exact matches). This may go without saying, but if you want exact matches remove the \* and if you want case sensitive, use the -name argument.


    0
    find . -iname \*${MYVAR}\* -print
    Buzzcp · 2010-08-04 05:43:51 0
  • This works fine too.


    0
    find "$1" -iname "*$2*"
    dbbolton · 2010-08-04 11:10:42 0
  • Sometimes you need the full path to your script, regardless of how it was executed (which starting directory) in order to maintain other relative paths in the script. If you attempt to just use something simple like: STARTING_DIR="${0%/*}" you will only get the relative path depending on where you first executed the script from. You can get the relative path to the script (from your starting point) by using dirname, but you actually have to change directories and print the working directory to get the absolute full path. Show Sample Output


    0
    STARTING_DIR=$(cd $(dirname $0) && pwd)
    bbbco · 2011-11-30 17:35:15 2
  • Since none of the systems I work on have readlink, this works cross-platform (everywhere has perl, right?). Note: This will resolve links. Show Sample Output


    0
    FULLPATH=$(perl -e "use Cwd 'abs_path';print abs_path('$0');")
    follier · 2013-02-01 20:09:34 0
  • Good for use in your ~/.bash_profile or a script. Show Sample Output


    0
    BOLD=$(tput bold); NORM=$(tput sgr0)
    thrifus · 2015-10-12 15:53:12 0
  • minimal oneliner to keep track of time Show Sample Output


    0
    read year month day hour minutes seconds epoch _ < <(date '+%Y %m %d %H %M %S %s')
    snorf · 2015-11-11 07:27:37 0
  • Normally executing 'set' returns a vast amount of information, including the source code of every function and variable within the environment - including those that are part of the shell. By using the -o posix argument, bash runs temporarily in POSIX mode for this command, which simplifies expressions and leaves out the shell's own functions and definitions - leaving a much smaller, more useful list. Show Sample Output


    0
    alias allvars=' ( set -o posix; set ) | less'
    incidentnormal · 2016-03-04 14:04:45 0
  • work for execute file


    -1
    dirname $(readlink -f ${BASH_SOURCE[0]})
    unixyangg · 2011-12-02 16:10:38 0
  • tail() { thbin="/usr/bin/tail"; if [ "${1:0:1}" != "-" ]; then fc=$(($#==0?1:$#)); lpf="$((($LINES - 3 - 2 * $fc) / $fc))"; lpf="$(($lpf<1?2:$lpf))"; [ $fc -eq 1 ] && $thbin -n $lpf "$@" | /usr/bin/fold -w $COLUMNS | $thbin -n $lpf || $thbin -n $lpf "$@"; else $thbin "$@"; fi; unset lpf fc thbin; } This is a function that implements an improved version of tail. It tries to limit the number of lines so that the screen is filled completely. It works with pipes, single and multiple files. If you add different options to tail, they will overwrite the settings from the function. It doesn't work very well when too many files (with wrapped lines) are specified. Its optimised for my three-line prompt. It also works for head. Just s/tail/head/g Don't set 'thbin="tail"', this might lead to a forkbomb.


    -1
    tail() { thbin="/usr/bin/tail"; if [ "${1:0:1}" != "-" ]; then fc=$(($#==0?1:$#)); lpf="$((($LINES - 3 - 2 * $fc) / $fc))"; lpf="$(($lpf<1?2:$lpf))"; [ $fc -eq 1 ] && $thbin -n $lpf "$@" | /usr/bin/fold -w $COLUMNS | $thbin -n $lpf || $thbin -n $lpf...
    fpunktk · 2012-03-23 19:00:30 0
  • Consider the following simple situation [ reading something using while and read ] [See script 1 in sample output] --------------------------------------------------- The variable var is assigned with "nullll" at first. Inside the while loop [piped while] it is assigned with "whillleeee". [Onlly 2 assignments stmts]. Outside the loop the last assigned value for "var" [and no variable] inside the while can't be accessed [Due to pipe, var is executed in a sub shell]. In these type of situation variables can be accessed by modifying as follows. [See script 2 in sample output] ___________________________ Vary helpful when reading a set of items, say file names, stored on a file [or variable] to an array an use it later. Is there any other way 2 access variables inside and outside the loop ?? Show Sample Output


    -5
    while read line; do echo $line; done <<< "$var"
    totti · 2011-09-22 16:53:32 0

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Check how far along (in %) your program is in a file
Say you're started "xzcat bigdata.xz | complicated-processing-program >summary" an hour ago, and you of course forgot to enable progress output (you could've just put "awk 'NR%1000==0{print NR>"/dev/stderr"}{print}'" in the pipeline but it's too late for that now). But you really want some idea of how far along your program is. Then you can run the above command to see how many % along xzcat is in reading the file. Note that this is for the GNU/Linux version of lsof; the one found on e.g. Darwin has slightly different output so the awk part may need some tweaks.

Convert CSV to JSON
Replace 'csv_file.csv' with your filename.

Update your OpenDNS network ip
Intended for dynamic ip OpenDNS users, this command will update your OpenDNS network IP. For getting your IP, you can use one of the many one-liners here on commandlinefu. Example: I use this in a script which is run by kppp after it has successfully connected to my ISP: --- #!/bin/bash IP="`curl -s http://checkip.dyndns.org/ | grep -o '[[:digit:].]\+'`" PW="hex-obfuscated-pw-here" if [ "$IP" == "" ] ; then echo 'Not online.' ; exit 1 else wget -q --user=topsecret --password="`echo $PW | xxd -ps -r`" 'https://updates.opendns.com/nic/update?hostname=myhostname&myip='"$IP" -O - /etc/init.d/ntp-client restart & fi --- PS: DynDNS should use a similar method, if you know the URL, please post a comment. (Something with members.dyndns.org, if I recall correctly)

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Quick HTML image gallery from folder contents
Setting: You have a lot of jpg files in a directory. Maybe your public_html folder which is readable on the net because of Apache's mod_userdir. All those files from the current folder will be dropped into a file called gallery.html as image tags that can be viewed within a web browser locally or or over the Internet. Original: $find . -iname "*.jpg" -exec echo "" >> gallery.html \;

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Calculating number of Connection to MySQL


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