Commands by johnraff

Commands by johnraff (5)

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Selecting a random file/folder of a folder

Choose random file from current folder. Avoids using ls.
This is sample output - yours may be different.
-2

for i in *; do echo "$i"; done | shuf -n1

johnraff · 2011-03-17 17:48:42 7
recursive search and replace old with new string, inside files

If you can install rpl it's simpler to use and faster than combinations of find, grep and sed. See man rpl for various options. time on above operation: real 0m0.862s, user 0m0.548s, sys 0m0.180s using find + sed: real 0m3.546s, user 0m1.752s, sys 0m1.580s Show Sample Output
This is sample output - yours may be different.
```
john@raffles2:~/Desktop$rpl -R LOCALE LOC**E copy\ of\ ies4linux-2.99.0.1/ 
Replacing "LOCALE" with "LOC**E" (case sensitive) (partial words matched)
..............................................................
A Total of 189 matches replaced in 62 files searched.
```
3

$rpl -R oldstring newstring folder

johnraff · 2009-12-09 03:15:31 14
Make sure a script is run in a terminal.

If your script needs to be run in a terminal, this line at the top will stop it running if you absent-mindedly double-click the icon, perhaps intending to edit it. (Of course this won't help with scripts that run in the background.)
This is sample output - yours may be different.
0

tty > /dev/null 2>&1 || { aplay error.wav ; exit 1 ;}

johnraff · 2009-11-04 16:18:00 6
A function to find the newest file of a set.

Usage example: newest Desktop/* Replace "-nt" with "-ot" for oldest. Run shopt -s dotglob first to include dotfiles.
This is sample output - yours may be different.
1

newest () { candidate=''; for i in "$@"; do [[ -f $i ]] || continue; [[ -z $candidate || $i -nt $candidate ]] && candidate="$i"; done; echo "$candidate"; }

johnraff · 2009-10-29 17:35:01 3
Run a file system check on your next boot.

The empty file /forcefsck causes the file system check fsck to be run next time you boot up, after which it will be removed. This works too: sudo >/forcefsck
This is sample output - yours may be different.
38

sudo touch /forcefsck

johnraff · 2009-10-29 17:04:47 19

What's this?

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Change wallpaper

list block devices

Shows all block devices in a tree with descruptions of what they are.

dmesg with colored human-readable dates

Use sed to color the output of a human-readable dmesg output

Check syntax of all Perl modules or scripts underneath the current directory

Finds all *.p[ml]-files and runs a perl -c on them, checking whether Perl thinks they are syntactically correct

Calculate days on which Friday the 13th occurs (inspired from the work of the user justsomeguy)

Friday is the 5th day of the week, monday is the 1st. Output may be affected by locale.

Insert a line at the top of a text file without sed or awk or bash loops

Yet another way to add a line at the top a of text file with the help of the tac command (reverse cat).

Linux clear restrictions of a user's password

Command that clears the expiration restrictions of a user's password

Show your local ipv4 IP

To show ipv6 instead, use [[ -6 ]] instead of [[ -4 ]] $ip -o -6 a s | awk -F'[ /]+' '$2!~/lo/{print $4}' To show only the IP of a specific interface, in case you get more than one result: $ip -o -4 a s eth0 | awk -F'[ /]+' '$2!~/lo/{print $4}' $ip -o -4 a s wlan0 | awk -F'[ /]+' '$2!~/lo/{print $4}'

Screensaver

Console screensaver.

Using numsum to sum a column of numbers.

numsum is part of of the num-utils package, which is available in some Linux distros and can also be downloaded at http://suso.suso.org/xulu/Num-utils. It contains about 10 different programs for dealing with numbers from the command line. Obviously you can do a lot of things that the num-utils programs do in awk, sed, bash, perl scripts, but num-utils are there so that you don't have to remember the syntax for more complex operations and can just think: compute the sum, average, boundary numbers, etc.

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