Commands using true (25)

  • It takes the first value of /prov/loadavg to print that many stars followed by the value. Show Sample Output

    while [ true ]; do cat /proc/loadavg | perl -ne 'm/(^[^ ]+)/; $L = $1; print "*" x $L; print " $L\n";' ; sleep 6; done
    t3o · 2017-10-13 06:47:06 2
  • This takes a picture (with the web cam) every 5 minutes, and send the picture to your e-mail. Some systems support mail -a "References: " so that all video surveillance emails are grouped in a single email thread. To keep your inbox clean, it is still possible to filter and move to trash video surveillance emails (and restore these emails only if you really get robbed!) For instance with Gmail, emails sent to can be filtered with "Matches:" Show Sample Output

    while true ; do fswebcam -d /dev/video0 -r 1280x1024 -F 15 - | uuencode $(date +\%Y\%m\%d\%H\%M).jpeg | mail -s "Video surveillance" ; sleep 300 ; done
    pascalv · 2016-08-09 14:22:45 0
  • (In French) Connection aux hotspots FreeWifi, et maintien de la connection active

    while true ; do wget --quiet --no-check-certificate --post-data 'login=my_account_number&password=my_password&submit=Valider' '' -O '/dev/null' ; sleep 600; done
    pascalv · 2016-07-23 16:34:42 1
  • `while true`: do forever `nc -l -p 4300 -c 'echo hello'`: this is the but anything can go here really `test $? -gt 0 && break`: this checks the return code for ctrl^c or the like and quite the loop, otherwise in order to kill the loop you'd have to get the parent process id and kill it. Show Sample Output

    while true ; do nc -l -p 4300 -c 'echo hello'; test $? -gt 0 && break; done
    rawco · 2016-03-22 21:55:44 0
  • it's nice to be able to use the command `ls program.{h,c,cpp}`. This expands to `ls program.h program.c program.cpp`. Note: This is a text expansion, not a shell wildcard type expansion that looks at matching file names to calculate the expansion. More details at I often run multiple commands (like apt-get) one after the other with different subcommands. Just for fun this wraps the whole thing into a single line that uses brace expansion.

    echo apt-get\ {update,-y\ upgrade}\ \&\& true | sudo bash
    alecthegeek · 2015-09-22 00:48:26 3
  • Generates labyrinth-like pattern on UTF-8 terminal in bash. For fun ;) Show Sample Output

    while ( true ) ; do if [ $(expr $RANDOM % 2 ) -eq 0 ] ; then echo -ne "\xE2\x95\xB1" ; else echo -ne "\xE2\x95\xB2" ; fi ; done
    tobi · 2015-01-17 12:46:37 3
  • If you have a client that connects to a server via plain text protocol such as HTTP or FTP, with this command you can monitor the messages that the client sends to the server. Application level text stream will be dumped on the command line as well as saved in a file called proxy.txt. You have to change 8080 to the local port where you want your client to connect to. Change also to the IP address of the destination server and 80 to the port of the destination server. Then simply point your client to localhost 8080 (or whatever you changed it to). The traffic will be redirected to host on port 80 (or whatever you changed them to). Any requests from the client to the server will be dumped on the console as well as in the file "proxy.txt". Unfortunately the responses from the server will not be dumped. Show Sample Output

    mkfifo fifo; while true ; do echo "Waiting for new event"; nc -l 8080 < fifo | tee -a proxy.txt /dev/stderr | nc 80 > fifo ; done
    ynedelchev · 2015-01-14 09:26:54 2
  • This will crop each page of the PDF by 10mm left, 11cm bottom, 22pts right, and nothing from the top.

    pdfjam --clip true --trim '10mm 11cm 22pts 0' m.pdf
    qdrizh · 2014-07-08 10:57:54 0
  • It is the best way i found to send a mail from the console in my centos server.

    true | mailx -n -a MYTEXT.txt -r -s log -S -S smtp-auth-user=MYUSER -S smtp-auth-password=MYPASSWORD
    xmuda · 2013-03-12 16:37:30 0
  • I use this loop for a variety of things. If a process won't die, I try to ask it nicely to let it die gracefully, and then i use killall and kill -9 to end its life. This will run the program killall and then start it again when it completes, indefinately.

    while true ; do killall mc ; done
    unixhero · 2012-04-13 08:03:41 0
  • combination of several of the above

    export GREP_COLOR='1;32';while [ true ]; do head -n 100 /dev/urandom; sleep .1; done | hexdump -C | grep --color=auto "ca fe"
    tbaschak · 2012-02-14 19:30:03 0
  • In this case it runs the command 'curl localhost:3000/site/sha' waiting the amount of time in sleep, ie: 1 second between runs, appending each run to the console. This works well for any command where the output is less than your line width This is unlike watch, because watch always clears the display. Show Sample Output

    while true ; do echo -n "`date`";curl localhost:3000/site/sha;echo -e;sleep 1; done
    donnoman · 2011-10-14 21:00:41 0
  • shell loop to scan netstat output avoiding loolback aliases (local/remote swap for local connections) Show Sample Output

    while true ; do sleep 1 ; clear ; (netstat -tn | grep -P ':36089\s+\d') ; done
    hute37 · 2011-09-28 11:39:43 2
  • Very simple web server listening on port 80 will serve index.html file or whatever file you like pointing your browser at http://your-IP-address/index.html for example. If your web server is down for maintenance and you'd like to inform your visitors about it, quickly and easily, you just have to put into the index.html file the right HTML code and you are done! Of course you need to be root to run the command using port 80.

    while true ; do nc -l 80 < index.html ; done
    ztank1013 · 2011-08-31 15:17:33 6
  • This is an example of the usage of pdfnup (you can find it in the 'pdfjam' package). With this command you can save ink/toner and paper (and thus trees!) when you print a pdf. This tools are very configurable, and you can make also 2x2, 3x2, 2x3 layouts, and more (the limit is your fantasy and the resolution of the printer :-) You must have installed pdfjam, pdflatex, and the LaTeX pdfpages package in your box. Show Sample Output

    pdfnup --nup 2x1 --frame true --landscape --outfile output.pdf input.pdf
    TetsuyO · 2010-12-21 14:20:06 0
  • This version works across on all POSIX compliant shell variants.

    Confirm() { echo -n "$1 [y/n]? " ; read reply; case $reply in Y*|y*) true ;; *) false ;; esac }
    eikenberry · 2010-11-22 16:54:16 0
  • Not as taxing on the CPU.

    while [ true ]; do head -n 100 /dev/urandom; sleep .1; done | hexdump -C | grep "ca fe"
    campassi · 2010-10-05 16:23:31 1
  • You can do some boolean logic like A or B then C else D using or : || and : && So you can do some : # false || false && echo true || echo false false # true || false && echo true || echo false true # false || true && echo true || echo false true # true || true && echo true || echo false true and so on ... I use it like : (ssh 'test something') || $(ssh 'test something') && echo ok || echo ko Show Sample Output

    true || false && echo true || echo false
    Sizeof · 2010-04-20 09:17:08 1
  • The shell has perfectly adequate pattern matching for simple expressions. Show Sample Output

    function ends_in_y() { case $(date +%A) in *y ) true ;; * ) false ;; esac } ; ends_in_y && echo ok
    unixmonkey9199 · 2010-04-06 22:18:52 0
  • Really bored during class so I made this... Basically, you hold period (or whatever) and hit enter after a second and you need to make the next line of periods the same length as the previous line... My record was 5 lines of the same length. It's best if you do it one handed with your pointer on period and ring on enter.

    count="1" ; while true ; do read next ; if [[ "$next" = "$last" ]] ; then count=$(($count+1)) ; echo "$count" ; else count="1" ; echo $count ; fi ; last="$next" ; done
    dabom · 2010-03-30 04:02:29 11
  • A bit different from some of the other submissions. Has bold and uses all c printable characters. Change the bs=value to speed up and increase the sizes of the bold and non-bold strings.

    echo -ne "\e[32m" ; while true ; do echo -ne "\e[$(($RANDOM % 2 + 1))m" ; tr -c "[:print:]" " " < /dev/urandom | dd count=1 bs=50 2> /dev/null ; done
    psykotron · 2009-12-19 19:05:04 1
  • This command produces the output of "du -sk testfile" in every 10 seconds. You can change the command to be whatever you want.

    while true ; do du -sk testfile ; sleep 10 ; done
    Solaris · 2009-08-14 11:39:52 2
  • Same as above but slooooow it down

    while true ; do IFS="" read i; echo "$i"; sleep .01; done < <(tr -c "[:digit:]" " " < /dev/urandom | dd cbs=$COLUMNS conv=unblock | GREP_COLOR="1;32" grep --color "[^ ]")
    friedchuckles · 2009-07-22 03:59:07 1
  • This will perform one of two blocks of code, depending on the condition of the first. Essentially is a bash terniary operator. To tell if a machine is up: ping -c1 machine { echo succes;} || { echo failed; } Because of the bash { } block operators, you can have multiple commands ping -c1 machine && { echo success; }|| { echo failed;; } Tips: Remember, the { } operators are treated by bash as a reserved word: as such, they need a space on either side. If you have a command that can fail at the end of the true block, consider ending said block with 'false' to prevent accidental execution Show Sample Output

    true && { echo success;} || { echo failed; }
    clockworkavian · 2009-04-02 01:49:25 1
  • I wrote a script called to delete the database, then load a new database with initial values. With this single-line shell loop, when I need to make a schema change (which happens often in the early stages of some projects), I hit ctrl-C to stop the running Django server, then watch do its thing, then watch the server restart. Show Sample Output

    while true ; do scripts/ ; ./ runserver ; done
    taurus · 2009-03-27 04:43:54 1

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Print text string vertically, one character per line.

Fastest segmented parallel sync of a remote directory over ssh
Mirror a remote directory using some tricks to maximize network speed. lftp:: coolest file transfer tool ever -u: username and password (pwd is merely a placeholder if you have ~/.ssh/id_rsa) -e: execute internal lftp commands set sftp:connect-program: use some specific command instead of plain ssh ssh:: -a -x -T: disable useless things -c arcfour: use the most efficient cipher specification -o Compression=no: disable compression to save CPU mirror: copy remote dir subtree to local dir -v: be verbose (cool progress bar and speed meter, one for each file in parallel) -c: continue interrupted file transfers if possible --loop: repeat mirror until no differences found --use-pget-n=3: transfer each file with 3 independent parallel TCP connections -P 2: transfer 2 files in parallel (totalling 6 TCP connections) sftp://remotehost:22: use sftp protocol on port 22 (you can give any other port if appropriate) You can play with values for --use-pget-n and/or -P to achieve maximum speed depending on the particular network. If the files are compressible removing "-o Compression=n" can be beneficial. Better create an alias for the command.

Command Line to Get the Stock Quote via Yahoo
Retrieve the current stock price from Yahoo Finance. The output is simply the latest price (which could be delayed). If you want to look up stock for a different company, replace csco with your symbol.

Batch edition of all Writer files in the current directory (body text)
This function does a batch edition of all OOO3 Writer files in current directory. It uses sed to search a FOO pattern into body text of each file, then replace it to foo pattern (only the first match) . I did it because I've some hundreds of OOO3 Writer files where I did need to edit one word in each ones and open up each file in OOO3 gui wasn't an option. Usage: bsro3 FOO foo

View any already in progress copy command in detail
If you spot a dubious looking cp command running you can use this command to view what is being copied and to where. 1234 is the PID of the cp command being passed to the lsof utility. 3r.*REG will display the file/directory that is being read/copied. 4w.*REG will display the destination it is being written to.

Generate random valid mac addresses
First set the variable $hexchars: $hexchars="0123456789ABCDEF" Change the number in the first for loop if you need less then 1200 mac addresses

Install pip with Proxy
Installs pip packages defining a proxy

Super Speedy Hexadecimal or Octal Calculations and Conversions to Decimal.
^Hexadecimal Ten minus Octal Ten is Eight(in Decimal). $ echo "$(( 0xaf )) = $(( 0257 ))" ^Hexadecimal AF and Octal 257 are both Decimal 175.

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"

find process associated with a port
e.g. fuser 25/tcp (see which pid is listening on smtp)

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